A special strike force of detectives will analyse footage from social media, CCTV and police-worn body cameras to identify and punish those who defied stay-at-home orders to protest against lockdown in Sydney.
NSW Police Minister David Elliott announced the formation of the 22-strong strike force on Saturday afternoon as he condemned the thousands of "very selfish boofheads" who earlier marched through the central business district.
"Police will be contacting people from tonight to have to answer for themselves and their behaviour, particularly the ringleaders," he vowed.
Premier Gladys Berejiklian said in a statement that she was "utterly disgusted" by the protesters who had shown "utter contempt for their fellow citizens".
"This type of activity during lockdown will not be tolerated and the full force of the law will be brought against anyone who engages in this type of illegal activity," she said.
In Sydney 57 people have already been charged and 90 infringement notices issued. Mr Elliott wants to see thousands of infringements issued.
He said he would be very surprised if the rally did not cause a spike of COVID-19 cases.
The thousands who joined the march between Sydney's Victoria Park and Town Hall should immediately get tested for COVID-19 for the benefit of their families and friends, Mr Elliott argued.
The protest occurred as daily case numbers rose to a new high for the year.
Some 163 cases were diagnosed in the 24 hours to 8pm on Friday, despite the government ratcheting up restrictions in the four weeks since Greater Sydney entered lockdown.
A number of police officers were injured as they were attacked by protesters, who threw plastic bottles and pot plants seized from the roadside at them.
Mr Elliott said police would crack down on protesters if they gathered again next weekend.
Police estimate 3500 people joined in the rally.
Despite a heavy police presence, including mounted and riot officers, protesters broke through a police barrier to continue down George St, but were stopped at King St.
Signs carried by the protesters called for "freedom" and "the truth".
Australia's deputy chief medical officer earlier warned that protesters were putting lives at risk.
"I'm very concerned if people are not following those restrictions ... When that happens, there is the risk that we'll get spread of COVID-19," Michael Kidd said on Saturday.
Meanwhile, in Melbourne, an anti-lockdown protest was brought to a violent end by police.
An AAP photographer wearing visible press accreditation was pepper sprayed as police cleared the rally, as were other photographers.
Thousands of protesters of all ages chanted "freedom" as they gathered outside Victoria's Parliament House.
Some lit flares. They held banners, including one that read: "This is not about a virus it's about total government control of the people."
Victoria Police said the event organisers had not been cooperative and would not consider moving the protest to a later, safer date.
Like their NSW counterparts, Victoria Police will review footage in an attempt to identify more of the protesters.
Six people have already been arrested and 67 people given penalty notices.
Police are also investigating an assault of a mounted police officer, after a protest threw a large bollard at her head.
In Adelaide, three people were arrested in anti-lockdown protests.
Hundreds also rallied in Brisbane on Saturday.
Australian Associated Press