Victorians face an anxious wait to see if the state government will enforce a snap lockdown on Greater Melbourne as health authorities scramble to contain a Covid-19 outbreak.
Acting Premier James Merlino told reporters on Wednesday morning the following 24 hours would be "critical" in learning whether further measures were required.
Professor Bruce Thompson, Dean of Health Sciences at Swinburne University, said if the current trend of infections continued, 30 cases could be announced on Thursday.
"You see this is starting to take off... that is how we know this virus works. I hope [30 cases] isn't the case," he told the ABC on Wednesday.
While confident 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.
He said any lockdown would be broad rather than confined to the city's northern suburbs, with confirmed cases travelling 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.
There are also fears for regional Victoria after a positive case visited Bendigo and Axedale, 150km away from the state capital.
A second AFL game was added as an exposure site after a case attended the North Melbourne-Essendon clash at Marvel Stadium on Sunday.
While the cluster has been genomically linked to a Wollert man who tested positive earlier this month after quarantining in a South Australia medi-hotel, the direct link between him and any of the new cases has not been found.
Restrictions imposed on Tuesday mean those in Greater Melbourne over 12 must wear masks in indoor public settings while home gatherings are reduced to five and public gatherings to 30.
Victoria last entered a five-day "circuit breaker" lockdown in February, when the virus escaped hotel quarantine and infected 13 people.
South Australia became the first state or territory to slam its border shut to Greater Melbourne, while NSW and Queensland are urging residents to reconsider travel to the city and parts of regional Victoria.
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