Melbourne, July 5 : Authorities in the Australian city of Melbourne on Sunday confined people living in nine housing estate tower blocks due to a sudden spike in the number of coronavirus cases. The city is putting "stage three" restrictions on 12 suburbs, reports the BBC. People there will only be able to leave the house for four reasons: work or education, exercise, medical care or care-giving, and shopping for supplies. But the nine tower blocks in Flemington and North Melbourne face a "hard lockdown". The 3,000 or so residents of the blocks are being told not to leave their homes for any reason for at least five days. At least 23 cases of infection were found on two estates in recent days. According to Victoria's Minister for Housing, Richard Wynn, some of the state's most vulnerable people live in the nine towers, and mental health and drug and alcohol support will be offered. The towers, he said, were characterised by having common lifts and common walkways, and they presented an "acute challenge going forward". Andrews said that it should take at least five days to test everyone in the towers. "We are extremely concerned that there are many hundreds of people in these towers who have already been exposed to the cases that we've found and possibly to cases that exist and that we haven't found," Deputy Chief Health Officer Annaliese van Diemen was quoted as saying by the BBC. "This is not just a matter of 23 to 30 odd people this is a matter of many hundreds who have already been exposed and who may already be incubating." Acting Chief Medical Officer Paul Kelly said a "new phase of the pandemic" was underway in Australia. "For the first time in Australia it's an actual complete lockdown," he was quoted as saying by the Sydney Morning Herald. While the infection numbers remain below Australia's peak in March, what concerns the authorities is that local transmission is now the key source of infections. Previously, most cases came from travellers returning from overseas. Australia has so far reported a total of 8,362 COVID-19 cases, with 104 deaths. /IANS