Police have put protesters on notice as anti-racist and anti-Islamist rallies are planned nationwide today.
The warning comes after violence erupted at sister rallies in Melbourne yesterday.
Specialist police officers will be deployed as hundreds of people in Sydney are expected to gather in Martin Place for the demonstrations.
New South Wales Police say they have worked with rally organisers to ensure the protests are conducted safely, but officers will respond swiftly to violent or disruptive behaviour.
Reclaim Australia has called supporters to gather for what organisers have described as “a public response to the shock of recent atrocities of Islam’s radicals both inside and outside of Australia”.
Hundreds are also expected to protest against bigotry, xenophobia and Islamophobia.
“We will not tolerate any criminal, anti-social or dangerous behaviour,” Assistant Commissioner Alan Clarke said in a statement.
“If you choose to do the wrong thing you’ll be removed and dealt with appropriately.
“The same goes for anyone who attempts to cause disharmony or incite conflict with those who may hold opposing views.”
The Sydney rallies are among a number planned in cities across Australia today including Canberra, Hobart and Perth.
In Queensland, a Reclaim Australia rally in Mackay is to be addressed by federal Coalition MP George Christensen.
Organisers of Rally Against Racism in Perth say they want to challenge Reclaim Australia without resorting to violence.
“We’re not going there with any intention of being violent in any way, we are actually there to challenge the violence, the ideological violence of the people in Reclaim Australia,” organiser Miranda Wood said.
“Hate speech is not welcome and we will be there to challenge it.”
The violent clashes in Melbourne saw hundreds of police called in and officers used capsicum spray to subdue the crowds.
Bottles were thrown and protesters from both sides were punched and kicked as they clashed.
Some masked protesters attempted to barge through the police blockade but were met with force as officers resisted.
In Adelaide there were tense scenes as Reclaim Australia and anti-racism demonstrators converged at Parliament House.
About 200 members of Reclaim Australia took to chanting, shouting and blaring loud music to get their message across and drown out the 400 or more opponents on the other side of the police barricade.