Australians have been told to stay away from beaches in three cities this weekend, especially in Sydney where the checkpoints created traffic jams and left some of the city's summer playgrounds subdued on a sweltering day a week before Christmas.
Andrew Scipione, deputy commissioner of New South Wales state police, said that about 1500 officers had been deployed to trouble spots.
"This is not a normal weekend," he said. "If nothing was to happen this weekend, we would deem our operation a success."
The clashes erupted last weekend in Cronulla beach, in Sydney's south, where thousands of white Australians attacked people of Middle Eastern appearance, and Lebanese and Muslim youths retaliated with two nights of violence.
"If you go there, you will be stopped ... We have never had to deal with a situation like this in the past"
deputy commissioner of New South Wales state police
Cronulla was quiet on Saturday, with just a sprinkling of sun-worshippers and surfers, but Scipione said police had "strong intelligence" that some groups planned disruptions on Sunday, possibly including neo-Nazis and white supremacist groups.
By Sunday, there will be about 2000 police on Sydney's beaches, Scipione said.
"We will be taking this very seriously," he said. "If you go there, you will be stopped ... We have never had to deal with a situation like this in the past."
Local media have portrayed the violence as a complicated clash of races and sub-cultures, starting with tension between Sydney's territorial surfing gangs and groups of Muslim youths using the same beaches.
It then drew in white supremacists who used the tension to pursue a wider, racist agenda.
During the violence, beach-goers have been attacked with crowbars, kicked and punched.
White Australians had attacked a
Middle Eastern-looking man
On Thursday, a Molotov cocktail was thrown at police. No one has been killed or seriously injured.
Racist text messages and emails have been circulating calling for violence this Sunday and local media have reported talk of Lebanese youths calling themselves the Lions of Lebanon coming from across the country to fight at the beaches this weekend.
Police also patrolled beaches north and south of Sydney along a 200km stretch of coastline, though there were no reports of violence on Saturday.