White supremacists from the Ku Klux Klan (KKK) group and anti-racism protesters clashed in the US state of California during rival demonstrations, with several people stabbed and injured in scuffles.

All four stabbing victims, including one suffering critical injuries, were part of a group that faced off with the rallying KKK members on Saturday in the city of Anaheim, police said.

"All hell broke loose," said Brian Levin, director of California State University, San Bernardino's Center for the Study of Hate and Extremism, who witnessed the violence. "I thought they were going to stomp these Klansmen to death."

Thirteen other members of both sides were arrested.

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

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The initial clash spurred several separate fights, Wyatt added, noting that two KKK members were stomped on by the crowd.

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Levin said the counter-protesters "smashed the side window of the Klan SUV and the front windshield... At that point, the crowd got extremely violent."

The Klan, which was formed in 1865, had up to four million members in the 1920s, but its membership has dwindled to between 5,000 and 8,000, according to the Southern Poverty Law Center.

Although it has historically targeted black people, the KKK has also launched attacks against Jews, immigrants, gays and lesbians. Until recently, it attacked Catholics as well.

Levin said he attended the rally as an observer, but ended up standing in between the Klansmen and the crowd of angry protesters to try to stem the violence.

"I helped two Klansmen get out of the way," said Levin."I told the crowd: Dr [Martin Luther] King wouldn't approve of this, please don't harm these men."

After pushing a Klansman away from the angry mob, Levin said he asked him: "How does it feel that your life was just saved by a Jewish man?" 

The man replied "thank you," according to Levin.

A member of the Ku Klux Klan salutes a lit cross during a ceremony in Virginia on October 11, 2014  [Reuters]

Source: Agencies