Thousands of residents in several high-rise apartments in Melbourne went into lockdown for at least five days Saturday, as officials struggle to control a virus outbreak in Australia's second biggest city.

Hundreds of police were deployed to enforce the lockdown of nine public housing towers, as the country recorded its biggest daily increase of coronavirus cases in months. The rise is driven almost entirely by 108 new cases in the southeast state of Victoria.

"There are many, many vulnerable people who live in these towers," Victorian Premier Daniel Andrews told media on Saturday. "Some of them will be returning home in the latter part of today, knowing that they will not be able to leave their home for a further five days."

The immediate lockdown in Melbourne's north would be a "massive logistical task" that includes supplying food to around 3,000 residents and deploying at least 500 police officers per shift, he added.

Victoria's Deputy Chief Health Officer Annaliese van Diemen said a number of cases had been detected in the towers, possibly exposing a highly vulnerable community with underlying health conditions. "The first priority here is to find every case in those towers, so that we don't have an explosion of infections," van Diemen said.

Victoria has ramped up testing and restrictions since a flare-up of cases last week. Another two Melbourne neighbourhoods were also told to stay at home from midnight Saturday, adding to the nearly 300,000 people put under restrictions on Tuesday.

The measures allow residents to leave their homes for essential reasons only, including for work and to buy food. The lockdowns were a "difficult but important step" Deputy Chief Medical Officer Paul Kelly said, ahead of an emergency meeting of top health officials on Saturday evening. "That rising number of active cases in Victoria is the major concern at the moment," Kelly told reporters in Canberra.

Twenty-five thousand tests were carried out in Victoria in 24 hours as officials increased efforts to trace, track and ultimately check the spread of the disease, Kelly said. Australia has managed to dodge the worst ravages of the virus and continues to roll back restrictions with more than 8,300 coronavirus cases and just over 100 deaths in a population of 25 million.