Three people died and seven were injured when the roof of a factory collapsed at Baba Mukand Singh Nagar here on Monday, officials said. Forty people, mostly labourers, were rescued from the site. Of the injured, the condition of three were stated to be critical, officials said, adding efforts were on to find out where more people were trapped under the debris. "The factory owner was lifting the lintel level without permission of the municipal corporation," Deputy Commissioner Varinder Sharma said. Teams of the National Disaster Response Force, State Disaster Response Force and civic body were undertaking the rescue operations.