Victoria has recorded another six local Covid-19 cases, bringing the cluster in Melbourne's north to 15.
The Department of Health reported 10 new local cases in the 24 hours to midnight, and Acting Premier James Merlino revealed another case had been identifed this morning.
The 10 cases announced by the health department included five cases reported yesterday, which were all part of the City of Whittlesea cluster.
Merlino said the new cases were close contacts of those already been identified.
"It's good that everyone is linked at this stage, but we are concerned about the number and also about the kind of exposure sites and the next 24 hours are going to be critical," he said.
Merlino said he could not rule out further restrictions in response to the outbreak.
"The next 24 hours are going to be particularly critical," he said.
"The message this morning is it's good that everyone is linked at this stage but we are concerned about the number and also about the kind of exposure sites and the next 24 hours are going to be critical if we're going to have to make further changes beyond the changes we announced yesterday."
There are now 23 active cases of the virus in Victoria.
The positive cases were detected from 26,180 test results.
The number of exposure sites is growing rapidly this morning, with two bars in Prahran recently listed as Tier 1 exposure sites for Saturday night.
Restrictions have been tightened across Greater Melbourne in response to the outbreak, and football fans who attended a Sunday afternoon AFL match at Melbourne's MCG sports ground were warned they may have been exposed to Covid-19 as one of the positive cases was at the venue.
The AFL has already been affected by the current outbreak with Western Bulldogs players and staff currently in isolation, pending negative Covid-19 tests.
Addressing the positive case that attended the AFL match between Collingwood and Port Adelaide on Sunday, Merlino said the AFL and MCC "have prepared for this moment".
"We're very grateful that we have the data on hand very shortly after it came to our attention so we could contact all those individuals and have them test and isolate until they receive a negative result, plus a small number who will need to quarantine," he said.