About 12 million people are under lockdown in Melbourne and Sydney (File) Melbourne, Australia: Australia's two largest cities are set to stay under tight Covid-19 restrictions as Melbourne on Monday extended a five-day snap lockdown designed to curb a virulent outbreak. "These restrictions simply cannot end at midnight tomorrow night," Victoria state premier Daniel Andrews said, without saying how long the Melbourne lockdown would last. About 12 million people are under lockdown in Melbourne and Sydney, where a month of restrictions has failed to quash an outbreak of the Delta variant. Australia had mostly dodged widespread community transmission in the 18 months since the pandemic began, but is now seeing more than 100 new cases a day, straining contact tracing efforts.