Three people have been stabbed, one critically, after a group of Ku Klux Klan members staging an anti-immigrant rally in southern California clashed with a larger gathering of counter-protesters.
The KKK had advertised plans for the rally in Anaheim's Pearson Park, about three miles from Disneyland, and about 30 anti-Klan protesters showed up beforehand, Anaheim police said.
When six Klan members arrived, they were attacked as they got out of their cars.
One Klansman stabbed a counter-protester with the decorative end of a flag pole, police said, setting off a vicious brawl in which Klan members and protesters fought across an entire city block.
Witness video shows Klansmen dressed in black shirts decorated with the Klan cross and Confederate flag being surrounded by counter-protesters as they arrive at the park in a car. A KKK member appears to hold out a flag pole to fend off the crowd.
"I got stabbed," a man is then heard screaming, lifting his T-shirt to show a wound to his stomach. A fire hydrant where the man briefly sat was covered in blood.
Police saw another Klan member with a knife in his hand and a counter-protester bleeding nearby, and took the KKK member into custody. Meanwhile, counter-protesters stamped on two KKK members, officers added.
"All hell broke loose," said Brian Levin, director of San Bernardino's Centre for the Study of Hate and Extremism at California State University. "I thought they were going to stomp these Klansmen to death."
Anaheim police had notified the public about the planned KKK protest and said they would be "monitoring the situation for any violations of law". The department also said that while the group's signs and fliers might be provocative, they are protected by the First Amendment.
Mr Levin said he did not see any uniformed officers at the park when the violence erupted. He said he tried to get between counter-protesters and Klansmen to help quell the melee until officers reached the scene.
"I'm still kind of a little bit shaken by it," he said.
Police Chief Raul Quezada defended the way his department handled the situation, saying a contingent of officers were dedicated to the gatherings and they arrested all of the main participants in the clash.
"Preventing violent confrontations is always our goal. Unfortunately the handful of individuals committed to criminal behaviour this afternoon caused the violent episode," he said in a statement.
Chris Barker, who identified himself as the "imperial wizard" of the Loyal White Knights of the Ku Klux Klan, said his members were holding a peaceful anti-immigration demonstration and acted in self-defence.
"If we're attacked we will attack back," said Mr Barker, who did not attend the rally and spoke by phone from North Carolina, where the organisation has its headquarters.
Last year, the group drew headlines when it protested over the removal of the Confederate flag from the South Carolina Capitol.
Twelve people were initially arrested, but five were released after investigators reviewed video of the confrontation, police said.
Those taken into custody were four Klansmen, who were booked for investigation of assault with a deadly weapon, and three counter-protesters on suspicion of stamping on an elderly Klan member.
The critically injured man was said to be in a stable condition.