The white supremacist rally was met by counterprotesters, Sacramento Fire Department spokesman Chris Harvey told AFP.
The fire department posted on Twitter that some of the patients had “critical trauma stab wounds.” It was unclear to which group the wounded belonged.
According to The Sacramento Bee newspaper, the stabbing spree broke out between some 25 neo-Nazis who had permission to protest on the capitol’s west steps and more than 150 anarchists and “anti-fascist” counterprotesters.
Videos and photos posted online showed the crowd grow violent, with some members clubbing others with what appeared to be bats or lumber, while still others threw rocks.
An injured and bloody black man lying on the sidewalk was attended to by members of the crowd in a video posted online by the Bee.
Two white men with blood dripping down their shaved heads were escorted by police in another clip on CNN.
Emergency responders received a call to the scene just before noon (1900 GMT).
The event was staged by a white-supremacist, anti-immigration group called the Traditionalist Worker Party.
A sister organization, the Golden State Skinheads, said online ahead of the rally that members would “stand our ground if forced to that point.”
After the protest Traditionalist Worker Party leader Matthew Heimbach said in a statement broadcast by CNN that “the anti-fascists used knives, bottles, bricks and chunks of concrete they broke off a construction site.”
“When they attacked, our men defended themselves to be able to drive the attackers off,” he said.
Protesters had cleared the capitol lawn by mid-afternoon, the Sacramento Fire Department reported.