NSW Premier Gladys Berejiklian has confirmed police have applied to the Supreme Court for tomorrow's rally against black deaths in custody, due to be attended by at least 10,000 people, to be "deemed illegal".
Only yesterday, she said protesting is an "inherent right in our democracy" and asked those taking to the streets "to do it peacefully" and maintain social distance.
At a press conference this afternoon, she said: "The NSW Government would never ever give the green light to thousands of people flagrantly disregarding the health orders."
"That never was and never will be our intention. Let me make it very, very clear that all of us have given up so much and worked so hard in order to make sure we get on top of the virus."
Outdoor public gatherings in NSW are limited to groups of 10 and a maximum of 500 people in shared spaces such as beaches and parks.
Earlier, Prime Minister Scott Morrison told people not to attend protests this weekend because it puts the "great gains" made against Covid-19 at risk.
Demonstrations are planned in solidarity with the Black Lives Matter movement and the death of African American man George Floyd at the hands of US police in May.
"The health advice is very clear, that it's not a good idea to go," Mr Morrison said.
"Let's find a better way and another way to express these sentiments, rather than putting your own health at risk, the health of others at risk, the great gains we have been able to make as a country in recent months.
"And let's not forget the terrible economic consequences of that as well, let's not put that at risk, let's exercise our liberties responsibly this weekend and encourage people not to attend for those reasons and those reasons only."
Victorian Premier Daniel Andrews urged people not to go, with the state's health minister Jenny Mikakos saying they were "concerned about the potential for a second wave".
Victoria Police deputy commissioner Shane Patton warned protest organisers they will be fined if their event goes ahead tomorrow in Melbourne.
The Herald Sun reports Patton said he hopes the event doesn't go ahead.
"People have to be held accountable for their actions," he said.
"We will issue infringements to the organisers."
Patton said the fines would not exceed A$1652.
Victoria has already recorded the most fines related to breaches of coronavirus directions.
Since late March in Victoria, individuals have faced fines of A$1652 and businesses A$9913 for failing to adhere to the chief health officer's directives "designed to slow the spread of Covid-19".
In a statement overnight, Australia's chief health officer Brett Sutton said the protest carried a "real risk" for all Victorians in the middle of a pandemic.
There are still cases of Covid-19 from community-to-community transmission being recorded in the state.
Meanwhile, South Australia's Police Commissioner Grant Stevens has approved an exemption from the state's coronavirus restrictions for protesters in Adelaide tomorrow.
Stevens, who is also the state coordinator under emergency management legislation, said he had taken the advice of the chief public health officer Nicola Spurrier and he believed the risk of community transmission was low.
Meanwhile, the family of Melbourne man Giuseppe Franzoni, 84, who died in April from Covid-19 have labelled protests planned on Saturday as disrespectful.
"What has happened in America is tragic, but we are going to see a second wave," a relative of Franzoni told The Herald Sun.
"It is total disrespect to the 102 Australians who have died so tragically. People just don't get it. They have a right to protest, but now is not the time."
Today show host Allison Langdon said while she backs the right to protest, she doesn't want to see the country's hard work battling Covid-19 fall apart.
"I am 100 per cent supportive of the right to protest but to be honest, not when we've worked so hard to get on top of this virus," she said on Friday morning.