About 300 people have been arrested during police crackdowns on protests at US universities.

In the early hours of Wednesday, police were called into Columbia University in New York, and also broke up protests at the University of California, Los Angeles (UCLA) as demos over the Israel-Hamas war reached boiling point. New York City Mayor Eric Adams said about 300 people were arrested at Columbia and nearby City College.

Columbia's Hamilton Hall was occupied by protesters and Mayor Adams said this particular group was "led by individuals who were not affiliated with the university". "There is a movement to radicalize young people," he said.

"And I'm not going to wait until it is done to acknowledge the existence of it." On the west coast, all classes at UCLA were cancelled on Wednesday due to "distress" caused by the overnight violence, according to a notice on its website. Students and staff have been advised to avoid Royce Quad, the area where clashes between pro-Palestinian and pro-Israeli protesters resulted in police wielding pepper spray being drafted in.

Pro-Palestinian protesters had erected barricades and plywood for protection, which counter-protesters tried to pull down. The protesters shoved and kicked one another, sometimes beating people with sticks or throwing chairs.

Read more:Why are students protesting? Sky News US correspondent Martha Kelner, reporting from UCLA, said: "Just look at this scene on a US university campus - California highway patrol wearing riot shields, riot masks, gas masks underneath their helmets." She said they were wearing gas masks "because throughout the course of the evening from inside this encampment, or at least the vicinity, a substance was released, I think, probably, pepper spray". "But the police here are not taking any chances, wearing gas masks - preparing, I guess, potentially to access this encampment." She said a protester appeared to pray at the feet of officers, adding: "She's a pro-Palestinian protester.

She's refusing to move for the California Highway Patrol. "She appears to be kneeling down, perhaps in prayer, at the feet of the patrol.

"It is a remarkable sight to see. These are scarcely fathomable scenes on a US university campus." By 5am local time, Kelner said the "volatile" situation at the campus had calmed down.

'Occupied, vandalised, and blockaded' On the other side of the country, police in riot gear raided Columbia University and arrested pro-Palestinian protesters occupying one of its buildings. About 30 to 40 people were removed from the Manhattan university's Hamilton Hall, according to police.

Those behind the protest said they had renamed the building "Hind's Hall" in honour of Hind Rajab, a six-year-old girl killed in a strike on Gaza in February. The raid came hours after Mayor Adams said the demonstration at the Ivy League school "must end now".

University bosses said they called in police after protesters "chose to escalate the situation through their actions". "After the university learned overnight that Hamilton Hall had been occupied, vandalised, and blockaded, we were left with no choice," a spokesman said.

"The decision to reach out to the NYPD was in response to the actions of the protesters, not the cause they are championing. "We have made it clear that the life of campus cannot be endlessly interrupted by protesters who violate the rules and the law." Demonstrators said they had planned to remain at the hall until the university conceded to the Columbia University Apartheid Divest's (CUAD) three demands: divestment, financial transparency and amnesty.

"Columbia will be proud of these students in five years," said Sweda Polat, one of the student negotiators for CUAD. A large group of officers dressed in riot gear entered the campus late on Tuesday evening.

Officers were also seen entering the window of a building via a police-branded ladder vehicle nicknamed "the bear". Protests have also spread to other campuses around the country.

Dozens were arrested on Monday at universities in Texas, Utah, Virginia, and New Jersey. The president of the University of Southern California, also based in Los Angeles, issued a statement on Tuesday after a swastika was drawn on campus.

"I condemn any antisemitic symbols or any form of hate speech against anyone," Carol Folt said. "Clearly it was drawn there just to incite even more anger at a time that is so painful for our community.

"We're going to work to get to the bottom of this immediately, and it has just been removed." National Security Council spokesperson John Kirby has said President Biden believes students occupying buildings was "absolutely the wrong approach" and "not an example of peaceful protest"..