Deputy Chief Health Officer Annaliese van Diemen said on Sunday the Black Lives Matter protest in Melbourne increased the risk for cases.

"In terms of potential outbreaks related to the protest, it really will be at least a week and probably closer to two weeks before we have an idea of whether there's been any transmissions or outbreaks related to that," Dr van Diemen said of Saturday's rally.

The impact will take its time to show due to incubation periods, people developing symptoms, getting tested and waiting for results, she said.

But the large number of people they don't have contact details for does "present a risk, and that is not an insignificant risk", she said.

Yet Dr van Diemen is "quietly hopeful" about Victoria's COVID-19 rates.

More than 10,000 protesters flooded Melbourne's CBD on Saturday in a show of solidarity for the US Black Lives Matter movement and to call for an end to Aboriginal deaths in custody.

Victoria Police will fine the Melbourne organisers $1652 each for breaching the directions of the chief health officer amid the pandemic.

Organisers Warriors of the Aboriginal Resistance posted online they were touched by supporters' offers to pay their fines, but preferred the money be directed to families directly affected by deaths in custody.

"We have enough networks and community to deal with this internally (if we even get a fine). Thank you VERY much for having our backs," the social media post reads.

A smaller, socially-distanced protest of about 20 people also went ahead outside of Frankston police station on Sunday morning.

Four new cases of coronavirus in Victoria were reported on Sunday, taking the state's recorded total to 1685.

Of the latest cases, one is a household contact linked to an outbreak last month at a McDonald's restaurant in Fawkner and the three others are returned travellers in hotel quarantine.

There are 177 confirmed infections acquired through unknown transmission, and 70 active cases in Victoria.

Six people are in hospital, two in intensive care.

To date, 1593 people have recovered from COVID-19 in Victoria.

While the wait is on to see what, if any impact, the mass protest has on infections, Dr van Diemen urged people not to attend gatherings of more than 20 people as per the health directions.

"Our advice has been that people don't attend gatherings of greater than 20 as per the current directions," she told reporters.

Dr van Diemen didn't attend the rally and refused to comment on the cause.

"I am not going to make comment on the cause," she said.

Dr van Diemen previously made a controversial tweet on April 29 where she likened COVID-19 to Captain Cook's arrival in Australia.

Australian Associated Press