Thousands of young white men have converged on Cronulla Beach in Sydney, Australia, and attacked people of Arabic and Mediterranean background.
There were angry confrontations between police and youths
Police and ambulance officers were pelted with beer cans and bottles, and an ambulance was attacked.
Several people were injured in the alcohol-fuelled violence, and at least 12 were arrested.
The authorities have condemned the outbreak of racial violence as "not the Australian way".
By Sunday night, the violence appeared to have spread to a second beach suburb, Maroubra, where men armed with baseball bats reportedly attacked cars.
And police said a man was stabbed in the back in south Sydney in what media reports said appeared to be further racial violence.
The clashes follow assaults a week ago on two volunteer lifeguards at the southern Sydney beach, reportedly by youths of Arabic and Mediterranean backgrounds.
Mobile phone text messages began circulating after the beatings, encouraging people to retaliate on Sunday and employing racial slurs.
Police Assistant Commissioner Mark Goodwin said innocent people had been targeted.
"The behaviour that's been seen down here at Cronulla today is nothing short of disgusting and disgraceful," he said. "It's certainly not the Australian way."
The area's Mayor, Kevin Schreiber, accused the mob of looking for a fight.
"As mayor and as a resident of Cronulla, I'm devastated by what has occurred on our beachfront," he said.
"It is the actions of a few, but let's not kid ourselves that people didn't come from far and wide to participate."
The president of the Islamic Friendship Association of Australia, Keysar Trad, accused the media of whipping up racial tension.
"Sections of the media took this issue far too far, and one can only surmise that the way these issues was dealt with on talk-back radio amounts to incitement," he said.
Sydney has many beaches, but Cronulla is one of a few that is easily accessible by train and is often visited by young people from the poorer suburbs of western and southern Sydney.
Area residents accuse the visitors of being disrespectful and of sometimes intimidating other beach-goers.