LOS ANGELES — Police removed barricades and began dismantling a pro-Palestinian demonstrators’ fortified encampment early Thursday at the UCLA campus after hundreds of protesters defied police orders to leave, about 24 hours after counter-protesters attacked a tent encampment on the campus.

The law enforcement action comes after officers spent hours threatening arrests over loud speakers if people did not disperse. Hundreds of people had gathered on campus, both inside a barricaded tent encampment and outside of it in support.

As police helicopters hovered overhead. The sound of flash-bangs, which produce a bright light and a loud noise to disorient and stun people, could be heard as police moved in, and chants of “where were you last night” could be heard.

Police methodically ripped apart the encampment’s barricade of plywood, pallets, metal fences and trash dumpsters and made an opening toward dozens of tents of demonstrators. Police also began to pull down canopies and tents.

Demonstrators were holding umbrellas like shields as they faced off with dozens of officers. Some of the protesters warned their fellow demonstrators to be ready with water in case police release tear gas or other irritant.

The police action occurred a night after the UCLA administration and campus police waited hours to stop the counter-protesters’ attack.

Demonstrators rebuilt the makeshift barriers around their tents on Wednesday afternoon while state and campus police watched.

The law enforcement response stands in contrast to the scene that unfolded the night before, when counter-demonstrators attacked the protesters’ encampment, throwing traffic cones, releasing pepper spray and tearing down barriers.

Fighting continued for several hours before police stepped in, though no arrests were made. At least 15 protesters suffered injuries, and the tepid response by authorities drew criticism from political leaders as well as Muslim students and advocacy groups, as well as Governor Newsom.

The chaotic scenes at UCLA came after New York police burst into a building occupied by protesters at Columbia University on Tuesday night, breaking up a demonstration that had paralyzed the school.

An Associated Press tally counted at least 38 times since April 18 where arrests were made at campus protests across the U.S. More than 1,600 people have been arrested at 30 schools.