The Whittlesea outbreak grew to 15 on Wednesday after another six cases were recorded overnight, sparking fears tougher restrictions were inevitable.

Acting Premier James Merlino hasn't ruled out ramping up restrictions, saying the 24 hours to Thursday morning is critical.

"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," he said

"I cannot rule out taking some further action, but we will update people as soon as we know."

Hundreds of people have turned out to be tested for coronavirus in Bendigo, about 150km north-west of Melbourne, after a hair salon in the town and the Axedale Tavern were listed as exposure sites.

Moving overseas, US President Joe Biden has met privately with the family of George Floyd on the first anniversary of his death.

Mr Floyd died after former police officer Derek Chauvin kneeled on his neck for more than nine minutes.

Chauvin, 45, was convicted of all three charges of murder and manslaughter over the deadly arrest and now faces up to 40 years in prison.

Mr Floyd was honoured with a moment of silence in many US cities including Minneapolis, the state where he died at the hands of police.

His sister, Bridgett, addressed the crowd that had gathered at a park only a few miles from where Mr Floyd died, saying it had been a troubling and long year.

"But we made it. They say with God all things are possible and I'm a true believer in that," she said.

"The love is very outpouring today. The love is here. George is here."

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