Los Angeles — A brawl erupted at UCLA after pro-Israel protesters tried to remove barricades at a pro-Palestinian encampment, and activists at the University of Wisconsin in Madison clashed with police officers who destroyed their tents, in a day of escalating violence on some college campuses over the war in Gaza.

The chaotic scenes unfolded Wednesday after police burst into a building occupied by anti-war protesters at Columbia University on Tuesday night, breaking up a demonstration that had paralyzed the school.

After a couple of hours of scuffles between dueling demonstrators at the University of California, Los Angeles, police wearing helmets and face shields separated the groups and restored calm. Later Wednesday, pro-Palestinian protesters rebuilt a barricade around their encampment. There were no counter-protesters in sight and law enforcement officers were deployed throughout the campus.

In Madison on Wednesday, police with shields removed all but one tent and shoved protesters, resulting in a scrum. Four officers were injured, including a state trooper who was hit in the head with a skateboard, according to University of Wisconsin police spokesperson Marc Lovicott.

Within hours, protesters had erected more tents at the UW campus.

More than 30 people were arrested, most of them released without charges, but four were charged with battering law enforcement, police said.

Tent encampments of protesters calling on universities to stop doing business with Israel or companies that support the war in Gaza have spread across campuses nationwide in a student movement unlike any other this century. The ensuing police crackdowns echoed actions decades ago against a much larger protest movement protesting the Vietnam War.

This is all playing out in an election year in the U.S., raising questions about whether young voters — who are critical for Democrats — will back President Joe Biden's reelection effort, given his staunch support of Israel.

There have been confrontations with law enforcement and more than 1,300 arrests. In rare instances, university officials and protest leaders struck agreements to restrict the disruption to campus life and upcoming commencement ceremonies.

The clashes at UCLA erupted when the pro-Palestinian protesters tried to expand their encampment late Tuesday night. Counter-protesters then tried to pull down the parade barricades, plywood and wooden pallets surrounding the encampment. In the chaos, firecrackers exploded.

Police left the scene around 11:30 p.m., and police in riot gear showed up at 1:45 a.m. to establish a perimeter. Pro-Israel protesters threw traffic cones and chairs, released pepper spray, and tore down barriers around the encampment. Some from the pro-Palestinian camp hopped over the barriers and scuffled with the counter-protesters.

Authorities have not detailed injuries. No one was arrested, and it’s not clear if all the demonstrators were students.

California Gov. Gavin Newsom, a Democrat, said anyone who engaged in illegal behavior at UCLA should be held accountable, including "criminal prosecution, suspension or expulsion.”

UCLA senior Edgar Gomez, who ventured outside his dorm to watch the ruckus unfold, said he saw counter-protesters tearing up Palestinian flags, and pepper spray hung in the air as the two sides fought.

“I’ve never seen this happen before," said Gomez, adding that he isn’t with either group. "I’ve never seen people get so heated.”

The university requested help and Los Angeles Mayor Karen Bass said city police officers were sent in. Newsom's spokesperson, Izzy Gardon, said the California Highway Patrol was also deployed after “unacceptable” delays in the university’s police force response to the clashes.

The nationwide campus demonstrations began at Columbia to protest Israel’s offensive in Gaza after Hamas launched a deadly attack on southern Israel on Oct. 7. Militants killed about 1,200 people, most of them civilians, and took roughly 250 hostages. Vowing to stamp out Hamas, Israel has killed more than 34,000 Palestinians in the Gaza Strip, according to the Health Ministry there.

Late Tuesday, New York City police officers entered Columbia's campus and cleared a tent encampment, along with Hamilton Hall where a stream of officers used a ladder to climb through a second-floor window, and police said protesters inside presented no substantial resistance. They had seized the Ivy League school building about 20 hours earlier.

Protesters first set up a tent encampment at Columbia almost two weeks ago. The school sent in police to clear the tents the following day, arresting more than 100 people. But the protesters returned.

Negotiations between the protesters and the college ground to a halt in recent days, and the school set a Monday deadline for the activists to abandon the tent encampment or be suspended.

Instead, protesters took over Hamilton Hall early Tuesday, carrying in furniture and metal barricades.

In a letter to senior police officials, Columbia President Nemat Shafik, who uses the first name Minouche, said the administration asked officers to remove protesters from the occupied building and a tent encampment “with the utmost regret.”

Columbia on Wednesday called Hamilton Hall “an active crime scene” under NYPD investigation and limited campus access to people with Columbia identification and essential personnel, barring the media.

“After the University learned overnight that Hamilton Hall had been occupied, vandalized, and blockaded, we were left with no choice,” the school said in a statement.

Fabien Lugo, a first-year accounting student who said he was not involved in the protests, said he opposed the university’s decision to call in police.

“This is too intense,” he said. “It feels like more of an escalation than a de-escalation.”

Blocks away from Columbia, at The City College of New York, demonstrators were in a standoff with police outside the public college’s main gate. Video posted on social media by reporters late Tuesday showed officers forcing some people to the ground and shoving others as they cleared the street and sidewalks.

After police arrived, officers lowered a Palestinian flag from the City College flagpole and tossed it to the ground before raising an American flag.

Close to 300 protesters were arrested in the crackdowns at Columbia and City College, officials said.

Brown University, another Ivy League school, reached an agreement Tuesday with protesters on its Rhode Island campus. Demonstrators closed their encampment after administrators agreed to consider a vote to divest from Israel in October — apparently the first U.S. college to agree to such a demand.

Meanwhile, at Northern Arizona University in Flagstaff, police in riot gear closed in on an encampment late Tuesday and arrested about 20 people for trespassing. University officials had warned that students would face criminal charges if they did not disperse.

First-year student Brayden Lang watched from the sidelines. “I still know very little about this conflict,” he said. “But the deaths of thousands is something I cannot stand for.”

Police also cleared an encampment Wednesday morning at Tulane University in New Orleans.

At Portland State in Oregon, school officials said some 50 protesters left a library on campus that had been occupied since Monday after administrators offered not to seek criminal charges or other discipline. An unknown number of people remained in the library Wednesday.

California State Polytechnic University, Humboldt, was tallying damage after police on Tuesday cleared protesters from two halls that they had occupied since early last week. Of those arrested, 13 are students, one is a faculty member and 18 are not students, the university said in a statement.

Israel and its supporters have branded the university protests antisemitic, while Israel’s critics say it uses those allegations to silence opposition. Although some protesters have been caught on camera making antisemitic remarks or violent threats, organizers of the protests, some of whom are Jewish, say it is a peaceful movement aimed at defending Palestinian rights and protesting the war.

Associated Press journalists around the country contributed to this report, including Cedar Attanasio, Jonathan Mattise, Stefanie Dazio, Jae Hong, Colleen Long, Karen Matthews, Sarah Brumfield, Carolyn Thompson, Philip Marcelo, Corey Williams and Felicia Fonseca.