Welcome to bbc news. An explosion on an underground train in south west london this morning is being treated as a terrorist attack. The train was packed with rush hour commuters when the blast went off. It sent a fireball through the carriage. 22 passengers were injured, none of them seriously. The device appears to have been in a white container with a timer. The mayor of london says a manhunt for the attacker is now underway. The device detonated at 820 this morning at Parsons Green station on the District Line in south west london. My colleague Matthew Price is there. Thank you very much indeed. The section of the London Tube Network on which this explosion took place is actually overground, not underground like much of the network. It is a couple of hundred metres behind me, down this road where, at the moment, police and forensic officers are going through the scene of the explosion to try and piece together what happened and what sort of device this was. We have already had some sort of analysis, through from the police on that, they called it an improvised explosive device, essentially a home made bomb. Eyewitnesses say there were wires coming out of a white builders bucket in a supermarket plastic shopping bag. We are also hearing from bbc sources that they believe there was a time of some sort attached to the device. As you say, it was exploded in the peak of the rush hour when many, many people were on the train, but perhaps because it happened at a train station above ground people could then get off the train quickly. Eyewitnesses spoke of panic on the platform in the moments after the explosion, but we do know that 22 people who were taken to hospital have what is referred to as blast injuries and we do not believe that anybody is in a serious or critical condition. It is worth reiterating that nobody was killed in this attack. We will take a report in amongst all the analysis we will getting in the next few moments. 8 20am this morning and the commuter ca ptu res 8 20am this morning and the commuter captures this on camera through the window of eightjune train. Captures this on camera through the window of eight june train. That bag is on fire. It is still a light, the remains of a makeshift bomb left amongst the passengers. Lets move away and get right down the platform. Seconds before, a flash of flame caused panic and serious burns. I heard a large bang from the doors on the other side of the tube train, then this fireball above my head has come and singed all of my hair. I have burn marks on the top of my head and everybodyjust ran off the train, and it was quite scary. Suddenly i heard a big bang, andl scary. Suddenly i heard a big bang, and i turned left and i saw the fireball surge towards and i turned left and i saw the fire ball surge towards my and i turned left and i saw the fireball surge towards my side. Then i heard a lady screaming and crying and people were very panicked. I heard a lady screaming and crying and people were very panickedm happened as the train was coming into Parsons Green station. People rushed to get out. I walked into the station and there was blood on the floor and people running down the stairs, screaming get out, people running and crying and the whole situation station was evacuated. People were coming out of the station coming covered in blood and burns. The bbc news presenter Sophie Raworth was nearby. Ive seen a woman who was just stretchered off here and clearly her legs wrapped up and she has been burned. She has burns to herface. She and she has been burned. She has burns to her face. She was conscious and was taking pain relief and oxygen. But clearly people have sustained a very nasty burns. She seemed to have burns all over her body, from top to toe. Her legs were wrapped up in some kind of protective plastic film and she definitely had burns on herface protective plastic film and she definitely had burns on her face as well, so very clearly people have been injured. The London AmbulanceService Began its emergency response. But early reports suggest that of 18 people taken to hospital, none have life threatening injuries. As police cordoned off large sections of the area there was disruption for local people. They can to read terry s investigation is now under way. A counterterrorism investigation. We now assessed that this was the debtor nation of an improvised explosive device detonation. As you have seen there are reports of 18 injuries and i understand most of them to be flash burns. The scene currently remains cordoned off and the investigation continues. Currently remains cordoned off and the investigation continuesm currently remains cordoned off and the investigation continues. It is a terrorist attack. The Police Services are now involved in a manhunt. The person or people responsible for this attack will be caught and brought to justice. The train was barely damaged. There was no blast. The device inside the carriage may have detonated prematurely. The bbc has been told it had a timer. From this crime scene, the investigation is spreading. The area has been secured and we have seen sniffer dogs checking, but nothing that nothing else has been left that might cause harm. The station sees clearly a majorforensic investigation but Intelligence Officers and counterterrorism detectives will be asking if they know already who may have planted the device, who might be involved, and they want to know if any further attacks are planned. It has become a weary routine this year. Local people we have spoken to and some of those on the train at the time i shaken, but there is a sense that this could have been far worse. A bomb in the corner of a tube train a p pa re ntly bomb in the corner of a tube train apparently not spotted by anyone. Police have again warned that there isa police have again warned that there is a need for calm, but also vigilance. As tom was saying there is an Extensive Police operation, and as the mair of london has told us, there is a manhunt. Our Home Affairs CorrespondentDaniel Sandford is at new Scotland Yard. Daniel, presumably the police focus is on cctv images, trying to work out who put this on the train. Yes, matthew. In a funny sort of way they have almost had a dry run for this. There was an attempt to blow up a tube train that failed and was detected at North Greenwich station last year, and that was also a timer device. What police did on that occasion was to work back through cctv images but also oyster cards and Contactless Cards. Im sorry, we seem to have lost daniel there, unfortunately. But he was explaining where the police are in their investigation at this moment, talking about other incidents which have helped them develop and hone their detective skills for moments like this. And there is an extensive cctv network, closed circuit security cameras across the capital. And especially on the underground network. So there will be a lot of material for them to go through. Just on a bit of the geography here, that tube line, which essentially runs right behind my back, behind the trees behind me, it comes from the west from wimbledon and heads into Central London in that direction. This train had come from wimbledon so there we re had come from wimbledon so there were only a few stops before it got here. Presumably therefore the cctv images from wimbledon and a couple of other stations before Parsons Green will be crucial. There have been lots of stories, notjust from the eyewitnesses, as inevitably and a lwa ys the eyewitnesses, as inevitably and always seems to happen like this, of people in local areas like this helping those who have been caught up helping those who have been caught up in all of the pandemonium. One of those who offered her support was 18 year old rachel green, who works in a cafe in Parsons Green. She described the moment when she realised the seriousness of what happened. It was not like an immediate sound that made me stop and drop everything, but we heard a small bang, but didnt think anything of it. Could it just bang, but didnt think anything of it. Could itjust be the train braking . But within minutes we had tens of people coming out of the station, looking distressed, in tea rs, station, looking distressed, in tears, and we noticed that there we re tears, and we noticed that there were people without shoes on or without their personal belongings, so we ran out of the copy shop and went to go and console them and ask if they were ok, get them water, tea, whatever they needed. Whatever we sure tea, whatever they needed. Whatever we sure saw was just shock among people today. I only saw very minor physical injuries and most of them we re physical injuries and most of them were coming from the rush from exiting the station, because as far as im aware, there was a huge commotion and a great deal of panic and we had a stampede coming out of the station to get out of the station once everybody knew there was an immediate danger. So most people were really upset from the uncertainty and the chaos and shock of that event, really. You said members of your family were close by as well. Yes, i have two younger siblings and they both take the train like me to School Every Day and trying to get in contact with them for the first ten minutes as i realised this was the time they usually commute, that was nerve racking. When i was able to make contact it was a great relief, but this is a quiet neighbourhood in london road. This is a family oriented area and the something to happen like this in our community was really shocking. How have you been feeling as it through the day about it . Been feeling as it through the day about it . We could knock comprehends what happened that first and when we saw people coming out of the station we were asking what has happened, but as more and more police and fire and Emergency Services arrived we began to realise the gravity of the situation, and i think a great deal of shock and sadness, but also a sense that london has some of the most resilient people in the world, and i think if we can get past this as we have been able to push past many incidents like this, that is what i hoped for. That is just incidents like this, that is what i hoped for. That isjust one of those who was here on the scene as that explosion took place and some of the help she gave to those who were caught up on the train. The police have just actually moved a bit of the police cordoned just in the last couple of moments also. It only gets a say few yards closer, but this is now the road that runs directly down to the site that explosion. We can get the reaction now from Richard Walton, former head of Counter Terrorism at Scotland Yard, who joins us from west london. Good afternoon to you. Good afternoon, yes. I know these are still early moments in this, but you will have seen some of the reporting of the nature of this device. I wonder what you make of it. Its very dangerous to speculate at this stage and my former colleagues will be keeping an open mind as to the nature of the attack. Clearly the bomb has not done what it was intended to do, kill and maim many people, so theres a sense of relief that the injuries are minor or not severe and life threatening. The bomb itself obviously looks many of the devices we have seen over the yea rs, the devices we have seen over the years, and also many of the devices that are on the Islamic State internet sites which inspire individuals to carry out attacks using home made bombs through readily available chemicals. Bbc sources are telling us that they are learning that this one may have had a timer on it. Again, a timer, if it has indeed got a timer, that is pretty much the norm in terms of home made devices. And it is what is recommended in the literature from the islamic extremist websites. That said, we should be careful about speculation that this is an islamic related attack. It might not be. You will recall back in may, earlier this year, a 20 year old man, david smith was given 15 Years Imprisonment for leaving a similar device such as this on a train at North Greenwich on thejubilee line in october. Again, the motive was not that clear. It looks like islamic related terrorism. On the face of it, it looks as much, but it could be a lone individual or it could be a lone individual or it could be a lone individual or it could be somebody as part of a cell. It could be the start of a campaign ora it could be the start of a campaign or a one off incident. We dont know at this stage and we should let the enquiry and investigation take its course. We heard earlier from the assista nt course. We heard earlier from the assistant commissioner for the metropolitan police who were saying that they have dozens of officers going through cctv images also asked the public to upload images to the website that they thought might be useful. Bearing in mind where the train had come from, just a few stops down the line, presumably, actually, by this stage the police could already, bearing in mind the size of this bucket, it would be difficult to hide it in a rucksack or coat, they may well already have images of the person they believe put it on the train. Indeed. It wont be long before they have images of one kind or another. Whether those images help them in the investigation is a moot point. We have to wait and see. But there is extensive coverage of cctv cameras across the network and has been for some time. It was obviously instrumental in identifying the attackers during the 7 7 attacks in 2005 some 15 years ago. Cctv evidence was critical in identifying those individuals, and it happened rabble daily rapidly, in a matter of days. Richard walton, thank you for your analysis. Lets speak to kevin hurley, former head of the Counter Terrorism and Public Order Department for the city of london police. Hes in our Central London studio. Good afternoon. I wonder what you make of the sort of understanding and picture we are building up of the nature of this device. And picture we are building up of the nature of this devicelj and picture we are building up of the nature of this device. I would go along very much with a lot of what Richard Walton has just said, but i disagree with his use of the phrase islamic. We need to be very careful in using that kind of term. It would be more appropriate to describe that as extremism. I urge course on with people using the word islamic, because that tends to two drive is lahm afobe, and we need to be much more careful islam are phobic reactions. Yes, it looks like it has failed to detonate correctly, just like the bombs did in 21 7, just like the bombs did in 21 7, just weeks after the 7 7 bombs. Who knows what the constituents of it are, but probably quite likely a mixture of trice atoned tri peroxide, but that would be conjecture, but it does tend to be the bomb of choice for these people at the present time and the Police Operation will be moving out as quickly as they can, to gather what evidence they can. One of the good things because it didnt go off properly, they have a treasure trove of forensic evidence to be found just with that particular bomb in terms of all kinds of tiny clues and hints that might be available on that. The next thing they will look to try and achieve is establish who was on the train, because ultimately might come down ascertaining which phones triggered which cctv mast as the train went by. So they will want to eliminate lots of phones on the train in order to find out perhaps if the bomber had a phone, and if it comes down to that they do not get him or her either fingerprints comes down to that they do not get him or her eitherfingerprints or dna on the partially exploded device, or, indeed, from cctv. Dna on the partially exploded device, or, indeed, from cctvi wonder, just moving away from the nature of the device and investigation, if you might think a little bit about what actually happened on this station. We know from eyewitnesses that the moment the explosion went off, the train doors opened and at that point there was, understandably for a couple of moments, some panic, people describe the rush to get out of the train station. Is there anything we can do that we should do in incidents like this to try smooth and smooth the escape this. Its relatively difficult in eight station that is relatively small. It would have been intended just go off but dashed off on the train wherever it was, but its very difficult to deal with that kind of situation with the standard phrase of keep calm and carry on, because people want to survive and panic will set in and they will try and run away from that. The bottom line is, the evidence of the manchester plane disaster is that those people who fought and pushed and climbed over seats are the ones who survived, so its difficult to say to people who are very scared, keep calm and stop pushing. Tragically, this is what happens. One of the great losses of life in the Second World War was when a v1 bomb landed on a cheap train underground shelter tube train underground shelter tube train underground shelter tube train underground shelter, and hundreds of people were killed in the stampede to escape. Its difficult to control Human Behaviour when they are in panic. Kevin, thank you very much for your time. We can now go back to Daniel Sandford, and we lost the line to him earlier. Daniel, i wonder if there is any latest information coming out from the police there . I think we will getan the police there . I think we will get an update from the metropolitan police later this afternoon. Its highly likely we will get another detailed statement of what it is they are prepared to say at this stage. Picking up on what Richard Walton, the guest before last, was saying. This is a dress there was a dress rehearsal for saying. This is a