A march by a neo-Nazi group outside California's Capitol in Sacramento descended into chaos on Sunday after the demonstrators were attacked by groups of counter-protesters.

Sacramento authorities said multiple people were stabbed in the melee, and described the situation as a "mass casualty incident."

In a statement posted on Twitter, the Sacramento Fire Department said five people were hospitalized, "some with critical trauma stab wounds." No arrests have been reported.

The Sacramento Bee reported that the clashes involved "around 150 anarchists and 'anti-fascist' protestors and about 25 neo-Nazis."

Video footage posted on social media showed masked counter-protesters clad in black wielding large wooden sticks and other makeshift weapons. Several people were shown being knocked down and beaten.

Insane video. Crowd sees any signs of "Nazis" and they run&attack. A lot of people bleeding/getting maced. @ABC10 pic.twitter.com/PoFhILfZ95

— Frances Wang (@ABC10Frances) June 26, 2016

VIDEO: Police stepping in to stop a man from being attacked. @ABC10 pic.twitter.com/Wzd9Q8zt1j

— Frances Wang (@ABC10Frances) June 26, 2016

Photos from the scene also showed blood spatters on the ground and areas marked off with crime scene tape.

"It's a highly volatile situation," Sacramento Police Chief Sam Somers said, according to the Sacramento Bee. He said other skinhead rallies had been held at the Capitol, but "this time the the anarchists have taken a much more aggressive stance to wreak havoc on the city."

The neo-Nazi event was organized by a group called the Traditionalist Workers Party, and a link posted on the group's Facebook page called it a protest "against globalization and in defense of the right to free expression." The group said it had obtained the necessary permits to march near the Capitol.

The Los Angeles Times reported that counter-protests were organized on social media. The Traditionalist Workers Party seemed to recognize the threat of violence ahead of the march. The group's Facebook page linked to a post that described the demonstration as a "march into the inferno" and referred to the possibility that a "mob" of opposition "may outnumber our men up to 10 to 1."

According to the Southern Poverty Law Center (SPLC), which tracks extremist groups in the US, the Traditionalist Workers Party formed in January 2015 as as the political wing of the Traditionalist Youth Network, "an identitarian-inspired umbrella group that aims to indoctrinate high school and college students into white nationalism." The SPLC described the Traditionalist Youth Network as "virulently racist and anti-Semitic."