Protesters started leaving the site roughly two hours after the attack began and police had established control as day broke on Wednesday morning. It is unclear whether police made any arrests.

Governor Newsom condemned the violence in a post on X, formerly Twitter, separate to his office's statement.

"The law is clear," he said. "The right to free speech does not extend to inciting violence, vandalism or lawlessness."

He said those responsible "must be held accountable... including through criminal prosecution, suspension, or expulsion".

Citing law enforcement sources, the Los Angeles Times reports there were only a few UCLA police officers on hand and they retreated because they were outnumbered by the crowd.

According to the newspaper, reinforcements were called from California Highway Patrol and Los Angeles and it took three hours to bring the situation under control.

The overnight clash at one of America's top public colleges took place only hours after police in New York City raided and cleared a Columbia University building taken over by students.

Protests at Columbia against the war in Gaza have inspired similar actions at universities - small and large, public and private - in more than two dozen states, with activists demanding that institutions cut financial ties with Israel and companies profiting from the war.

On Wednesday, state troopers arrested 17 anti-war protesters at the University of Texas at Dallas, said the BBC's Tom Bateman on campus, while the NYPD arrested at least 15 people at Fordham University in the Bronx.

UCLA cancelled classes on Wednesday, as it sought to ease tensions on the central quad of its Westwood campus.

Mary Osako, a UCLA vice-chancellor, said police and other first responders were called to the scene of its encampment over "horrific acts of violence" early on Wednesday morning.

"We are sickened by this senseless violence and it must end," she said.

Los Angeles Mayor Karen Bass slammed the clashes as "absolutely abhorrent and inexcusable". Speaking later on Wednesday, she called for an investigation into the violence.

"Those involved in launching fireworks at other people, spraying chemicals and physically assaulting others will be found, arrested and prosecuted, as well as anyone involved in any form of violence or lawlessness," she said.

By morning, a tight security cordon was in place as a handful of protesters fortified their encampment.