Up to 4000 people are expected to gather in Victoria Square on Saturday before marching through the city in support of the global calls for justice for US man George Floyd, who died while being arrested in Minneapolis.

Commissioner Grant Stevens says the exemption from emergency provisions will allow the event to go without breaching COVID-19 restrictions, but those taking part must still be mindful of their own health and the health of others.

He said protesters were urged to abide by social distancing rules as far as possible and ensure proper hygiene is in place.

People feeling sick are encouraged not to attend.

"This is a unique and extraordinary event. There is a sentiment that suggests people should have a right to protest on significant matters," Mr Stevens said on Friday.

"We acknowledge that and there is also the reality that with significant numbers of people attending, that the potential to prevent it occurring is also a very difficult challenge for police.

"We do not want to see confrontation with people who are deliberately breaching a direction under the Emergency Management Act and the decision has been taken to eliminate that factor by providing the exemption."

Mr Stevens said police were keen to work with the organisers of the protest to ensure it remained peaceful but had been unable to make contact so far.

He said police would also be prepared to deal with any unlawful activity, particularly any harm being caused to individuals.

According to the event's Facebook page, the death of Mr Floyd had sparked "heroic" uprisings in the US.

"Black, Brown and other working-class people are fighting back against a system that doesn't care whether they live or die," the post said.

It said the event in Adelaide was also a protest against racism, and the murder of black people in Australia.

But it also asked those attending to wear masks and said social distancing would be enforced.

Australian Associated Press