Melbourne residents are about to find out if a growing coronavirus cluster in the city's north will trigger another lockdown in the Victorian capital.
Acting Premier James Merlino raised the prospect of a shutdown on Wednesday after the so-called Whittlesea cluster expanded to 15 cases.
Mr Merlino did not rule out further action, ahead of a cabinet meeting on Wednesday night.
While authorities have "run down multiple generations of transmission", Chief Health Officer Brett Sutton is concerned about the amount of time positive cases have been out in the community.
Any lockdown would be broad rather than confined to the city's northern suburbs. Some of the confirmed cases travelled to Bendigo and as far north as Cohuna on the NSW border.
"We've got significant spread of exposure sites at the moment so it's not something that we would look to at a postcode level," Prof Sutton said.
As of Thursday morning, there were 79 exposure sites listed on the Health Department's website, spread across more than 30 Melbourne suburbs and regional Bendigo, Cohuna and Red Hill.
The MCG and Marvel Stadium are amongst the exposure sites and three inner-suburban nightclubs remain a "concern".
An infected person attended the Collingwood-Port Adelaide AFL game at the MCG on Sunday, while one was also at the North Melbourne-Essendon clash at Marvel Stadium later that same day.
A decision on crowd limits for this weekend's AFL matches in Melbourne has been delayed and the RISING festival has been cleared to go ahead, for now.
A number of restrictions were introduced for Greater Melbourne on Tuesday evening, including gathering limits of five people at homes and 30 in public and mandatory masks indoors.
Genomic sequencing shows the City of Whittlesea outbreak is linked to the case of a Wollert man, who contracted the virus in quarantine in South Australia earlier this month.
A report released on Wednesday in SA found it likely he caught the virus through aerosol transmission due to the "timing of doors opening and closing" at an adjacent room occupied by an infected guest.
SA on Wednesday became the first state to close its border to residents of Greater Melbourne. NSW and Queensland are urging residents to reconsider travel to the city and parts of regional Victoria.
Victoria's last lockdown was for five days in February, after the virus escaped hotel quarantine and infected 13 people.
It was the state's third lockdown since the coronavirus pandemic began last year.
© AAP 2021
Photo: Victorian Chief Health Officer Brett Sutton (AAP Image/Erik Anderson)