Law enforcement officers have massed by the hundreds on the campus of the University of California at Los Angeles after darkness fell, in preparation to clear out a pro-Palestinian protest camp attacked the night before by pro-Israel supporters.

Live television footage showed police in tactical gear filing onto the UCLA campus adjacent to a complex of tents occupied by throngs of demonstrators.

Some of the activists were seen donning hard hats, goggles and respirator masks in anticipation of the raid a day after the university declared the encampment unlawful.

Hundreds of other pro-Palestinian activists assembled outside the tent city jeered police with chants of "Shame on you," some banging on drums and waving Palestinian flags, as officers marched onto the campus grounds. Many of the demonstrators wore the traditional Palestinian keffiyeh scarves.

Pro-Palestine supporters band together at UCLA as police presence builds. – Reuters

Before moving in, police with a loudspeaker urged the demonstrators to clear the protest area in a grassy plaza between the landmark twin-tower auditorium Royce Hall and the main undergraduate library.

UCLA had canceled classes for the day following a violent clash late Tuesday night and early Wednesday morning between the encampment's occupants and a group of masked counter-demonstrators who mounted an assault on the tent city with sticks and poles.

The occupants of the outdoor protest camp, set up last week, had remained otherwise largely peaceful before the melee, which university officials blamed on "instigators," vowing an investigation.

Pro-Palestinian protesters say they were 'violently attacked' on UCLA campus. – Reuters

Wednesday evening's raid also came a day after police in New York City arrested pro-Palestinian activists who occupied a building at Columbia University and removed a tent city from the campus of the Ivy League school.

Police arrested about 300 people at Columbia and City College of New York, Mayor Eric Adams said. Many of those arrested were charged with trespassing and criminal mischief.

The clashes at UCLA and in New York are part of the biggest outpouring of US student activism since the anti-racism rallies and marches of 2020.

The protests follow the October 7 attack on southern Israel by Hamas militants from the Gaza Strip and the ensuing Israeli offensive on the Palestinian enclave.

Pro-Palestinian protesters in New York City decry police, university responses. – AP

Students have rallied or set up tent encampments at dozens of schools across the US in recent days, expressing opposition to Israel's war in Gaza and demanding schools divest from companies that support Israel's government. Many of the schools have called in police to quell the protests.

With the presidential election coming in November, Republican lawmakers have accused some university administrators of ignoring anti-Semitic rhetoric and harassment, and some have demanded Columbia's president Minouche Shafik resign.

Many protesters, some of whom are Jewish, reject allegations of anti-Semitism. Shafik has said the protests have brought rancor to life at Columbia, while also blaming some episodes of harassment and hostile rhetoric on outsiders drawn to the busy Manhattan streets surrounding the campus.

US President Joe Biden, who has angered many protesters by funding and arming Israel, plans to give a speech on anti-Semitism next week at a Holocaust memorial event.

"Americans have the right to peacefully protest," Karine Jean-Pierre, the White House spokesperson, said. "Forcibly taking over a building is not peaceful."

Republican US presidential candidate Donald Trump said it “was a beautiful thing to watch” New York police officers raiding the Columbia University building occupied by pro-Palestinian students, and called on officials to crack down on campus protests across the United States.

“New York was under siege last night,” Trump told supporters at a campaign rally in Wisconsin, praising the police officers for arresting about 300 protesters, who he referred to as “raging lunatics and Hamas sympathizers.”

“I say remove the encampments immediately, vanquish the radicals and take back our campuses for all of the normal students who want a safe place from which to learn,” Trump said.

Palestinians express support for ongoing US college protests. – AP

Before the clashes in Los Angeles, UCLA officials declared that an encampment on its campus was unlawful, violated university policy and included people unaffiliated with the campus.

Afterwards, counter-demonstrators – many of them masked and some apparently older than most students – can be seen in videos throwing objects and trying to smash or pull down the wooden and steel barriers erected to shield the encampment.

Some screamed pro-Jewish comments as pro-Palestinian protesters tried to fight them off.

"I just didn't think they would ever get to this," said Kaia Shah, a pro-Palestinian protester and researcher at UCLA, "where our protest is met by counter-protesters who are violently hurting us, inflicting pain on us, when we are not doing anything to them".

Demonstrators on both sides used pepper spray, and fights broke out. Pro-Palestinian demonstrators said the counter-protesters threw flares at them and beat them with bats and sticks.

Benjamin Kersten, a UCLA graduate student and member of the pro-Palestinian group Jewish Voice for Peace, called it "a devastating night of violence."

"The encampment would be a peaceful effort were it not for the continuous presence of counter-protesters and agitators," he said.

Police said UCLA had called them to restore order and maintain public safety "due to multiple acts of violence" within the encampment. Broadcast footage later showed police clearing a central quad beside the encampment and erecting a metal crowd control barrier in front of it.

The atmosphere was calmer on Wednesday. Hundreds of police officers were on campus and lining its perimeter. It was unclear how many arrests were made or the number of people injured.

Students speak out about overnight violence at UCLA protests. – AP

Columbia's Shafik said she had asked police to stay on campus until at least May 17, two days after graduation, and the main campus, where student dorms are located, remained under lockdown on Wednesday.

The school said the rest of the semester would be conducted remotely, including final exams.

Ararat Sekeryan, a sixth-year Slavic languages doctoral student from Istanbul, described being pushed out of the lawn encampment and described the calling of police as dangerous.

"I myself felt attacked," he said. "They were so afraid of this peaceful movement that they had to send more than a thousand, maybe hundreds of police to campus."

Ben Solomon, a 22-year-old Jewish student at Columbia, said he welcomed the move to clear what he called a "mob" from the occupied building and encampment.

"I'm glad to see universities took decisive action," he said, as more than 100 students and professors gathered in a street adjoining the campus to protest the school's decision to call the police.

The university earlier warned that students involved in the occupation faced academic expulsion.

Gaza student protest is 'a much bigger movement', says leader of Columbia protests in 1968. – Reuters