Three people were stabbed, one of them critically, and 13 others were arrested in California on Saturday when a Ku Klux Klan rally erupted into clashes with counter-protesters.

Three people were stabbed, one of them critically, and 13 others were arrested in California on Saturday when a Ku Klux Klan rally erupted into clashes with counter-protesters, witnesses and police said.

Around midday, half a dozen members of the white hate group, whose ranks still number several thousand in the United States, arrived at the protest site in Anaheim, officials said.

At that point the Klan members were "swarmed" by protesters, who attacked them with at least one wooden plank, witness Brian Levin told AFP.

Local police spokesman Sergeant Daron Wyatt said it appeared that "six KKK people arrived and were immediately attacked by counter-protesters, which led to a counter-protester being stabbed."

The initial clash spawned several separate fights, Wyatt added, noting that the three stabbing victims were all counter-protesters, while another two KKK members were stomped by the crowd.

One of the victims, he said, was stabbed with the decorative end of a flagpole, according to The Orange County Register.

Of those arrested, six were KKK members and seven were from the rival demonstration, Wyatt said. All were men, except for one woman in each group.

The counter-protesters "smashed the side window of the Klan SUV and the front windshield," said Levin, who heads the Center for the Study of Hate and Extremism at California State University in San Bernardino.