Ten people were wounded - two of them with life-threatening injuries - when protesters clashed with members of a white nationalist group in California.
Violence erupted outside the California state Capitol building in Sacramento, which was on lockdown until protesters cleared the area.
California Highway Patrol Officer George Granada said about 30 members of the Traditionalist Worker Party (TWP) gathered for a rally around noon on Sunday.
They were met by about 400 counter-protesters and a fight broke out.
As people tried to leave the area, smaller fights broke out, Mr Granada said.
The authorities were investigating what happened, but no arrests have been made.
Videos posted on social media showed mounted police officers dispersing a group of mostly young people, some with their faces covered.
Some were throwing stones at a man holding a stick and being shielded by police officers in riot gear.
Sacramento Fire Department spokesman Chris Harvey said nine men and one woman, ranging from 19 to 58-years-old, were treated for stab wounds, cuts, scrapes and bruises, and two were taken to hospital with life-threatening stab wounds.
"There was a large number of people carrying sticks and rushing to either get into the melee or see what was going on," he said.
The Southern Poverty Law Centre has described TWP as a group formed in 2015 as the political wing of the Traditionalist Youth Network, which aims to "indoctrinate high school and college students into white nationalism".
Matthew Heimbach, chairman of the Traditionalist Worker Party, told the Los Angeles Times that his group and the Golden State Skinheads organised the rally.
He said that in the clash, one of their marchers had been stabbed in an artery and six of the counter-protesters had also been stabbed.
Vice chairman Matt Parrott, who was not present at the rally, blamed "leftist radicals" for instigating the violence.
A post recently uploaded to the site of the Traditionalist Youth Network said TWP members planned to march in Sacramento to protest against globalisation and in defence of their right to free expression.
"We concluded that it was time to use this rally to make a statement about the precarious situation our race is in," the Traditionalist Youth Network statement said.
"With our folk on the brink of becoming a disarmed, disengaged, and disenfranchised minority, the time to do something was yesterday!"
The clash on Sunday follows a confrontation in March between Ku Klux Klan members and protesters in Anaheim, California in which three people were stabbed.