Activists at UCLA traded in fistfights and shoving, kicking and using sticks to beat one another during the fractious scenes.
Hours earlier, police carrying riot shields burst into a building at Columbia University that pro-Palestinian protesters took over and broke up a demonstration, arresting dozens.
After a couple of hours of scuffles between pro-Palestinian and pro-Israeli demonstrators at UCLA, police wearing helmets and face shields formed lines and slowly separated the groups.
The clashes at UCLA took place around a tent encampment built by pro-Palestinian protesters, who erected barricades and plywood for protection, while counter-protesters tried to pull them down.
Los Angeles Mayor Karen Bass called the violence "absolutely abhorrent and inexcusable".
Similar scenes played out earlier at Columbia University in New York, where dramatic footage showed police marching onto the campus in upper Manhattan to get into the campus’ Hamilton Hall to remove students.
Protesters had broken into the building in the early hours of Tuesday morning.
Within three hours the campus had been cleared of protesters, said a police spokesperson, adding "dozens" of arrests were made.
Police were seen loading dozens of detainees onto a bus, each with their hands bound behind their backs by zip-ties, the entire scene illuminated with flashing red and blue lights of police vehicles.
"Free, free, free Palestine," chanted protesters outside the building. Others yelled "Let the students go."
“Columbia will be proud of these students in five years,” said Sweda Polat, one of the student negotiators for Columbia University Apartheid Divest, the coalition of student groups that has organised the protests.
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She said students did not pose a danger and called on police to back down, speaking as officers shouted at her and others to retreat or leave campus.
Shortly after police moved in, Columbia University President Minouche Shafik released a letter in which she requested police stay on campus until at least May 17 - two days after graduation - "to maintain order and ensure that encampments are not re-established."
Protesters were seeking three demands from Columbia: divestment from companies supporting Israel's government, greater transparency in university finances, and amnesty for students and faculty disciplined over the protests.
President Shafik this week said Columbia would not divest from finances in Israel.
Instead, she offered to invest in health and education in Gaza and make Columbia's direct investment holdings more transparent.
In her letter released on Tuesday, Shafik said the Hamilton Hall occupiers had vandalised university property and were trespassing, and that encampment protesters were suspended for trespassing.
The university earlier warned that students taking part in the Hamilton Hall occupation faced being expelled.
The occupation began overnight when protesters broke windows, stormed inside and unfurled a banner reading "Hind's Hall," saying they were renaming the building for a six-year-old Palestinian child killed in Gaza by the Israeli military.
At an evening news briefing held a few hours before police entered Columbia, Mayor Eric Adams and city police officials said the Hamilton Hall takeover was instigated by "outside agitators" who lack any affiliation with Columbia and are known to law enforcement for provoking lawlessness.
Police said they based their conclusions in part on escalating tactics in the occupation, including vandalism, use of barricades to block entrances and destruction of security cameras.
One of the student leaders of the protest, Mahmoud Khalil, a Palestinian scholar attending Columbia's School of International and Public Affairs, disputed assertions that outsiders led the occupation.
"Disruptions on campus have created a threatening environment for many of our Jewish students and faculty and a noisy distraction that interferes with the teaching, learning and preparing for final exams," the university said in a statement on Tuesday before police moved in.
The October 7 attack on Israel by Hamas militants from Gaza, and the ensuing Israeli offensive on the Palestinian enclave, have unleashed the biggest outpouring of US student activism since the anti-racism protests of 2020.
Many of the demonstrations across the country have been met with counter-protesters accusing them of stirring up anti-Jewish hatred.
The pro-Palestinian side, including Jewish people opposed to Israeli actions in Gaza, say they are being unfairly branded as antisemitic for criticising Israel's government and expressing support for human rights.
The issue has taken on political overtones in the run-up to the US presidential election in November, with Republicans accusing some university administrators of turning a blind eye to antisemitic rhetoric and harassment.
White House spokesperson John Kirby on Tuesday called the occupation of campus buildings "the wrong approach."
New York Police Department officials had stressed before Tuesday night's sweep that officers would refrain from entering the campus unless Columbia administrators invited their presence, as they did on April 18, when NYPD officers removed an earlier encampment. More than 100 arrests were made at that time, stirring an outcry by many students and staff.
Dozens of tents, pitched on a hedge-lined grassy area - beside a smaller lawn since planted with hundreds of small Israeli flags - were put back up days later.