Officers began arresting protesters on the University of California Los Angeles campus early Thursday, detaining some with their hands zip-tied behind their backs.

Those who were detained appeared to have been moving willingly with officers, ABC News station KABC reported.

As law enforcement moved into the encampment, some of the protesters began chanting, repeating the phrase "Shame on you" in chorus.

-ABC News' Jenna Harrison and Kevin Shalvey

UCLA officials issued an evacuation order for all protesters in the area of Royce Quad, saying the encampment was "unlawful."

Smoke billowed around law enforcement officials as they began breaking through the barricades on the campus encampment. It was not immediately clear whether the smoke had been dispersed by the police or the protesters.

The encampment in Dickson Plaza, along with all unauthorized tents and structures, had been declared "unlawful," campus public safety officials said in an alert.

"The University requires that everyone must leave the encampment and adjacent areas, as well as all unauthorized structures and tents immediately, until further notice," the alert said.

-ABC News’ Amanda Morris and Kevin Shalvey

California Highway Patrol officers in riot gear streamed early Thursday onto the University of California Los Angeles campus.

The officers were met by a wall of protesters, who appeared unwilling to move. Officials had earlier ordered protesters to abandon their encampment.

Officers were working to tear down barricades of plywood boards that been erected along some of the edges of that encampment.

Los Angeles Police Department officers had earlier retreated from the encampment. At one point, LAPD and protesters briefly scuffled as officers made their way out of the encampment.

-ABC News' Amanda Morris and Kevin Shalvey

At least 90 people were arrested Wednesday during a protest on the campus of Dartmouth University, local police said.

The people who were arrested included both students and non-students, Hanover Police Department said in a statement released Thursday. Charges included criminal trespass and resisting arrest, police said.

Ahead of Wednesday's planned protest, campus security had warned demonstrators that tents or encampments wouldn't be allowed.

"Once tents were erected, Dartmouth Safety & Security made multiple announcements to participants that they must dispel, and they refused," Charles B. Dennis, Hanover's chief of police, said in a media release.

Hanover police and the New Hampshire State Police continued with "multiple" announcements, but some protesters refused to disperse, he said.

-ABC News' Jessica Gorman and Kevin Shalvey

Linda G. Mills, the president of NYU, posted a statement Friday evening explaining why the school called in the NYPD to break up an encampment on the Greene St. Walkway earlier in the day.

Mills said 14 people who refused orders to leave the area were arrested and the incident was non-violent.

The president said that the police were called in for numerous reasons, including noise complaints from nearby residents and businesses, safety concerns over the crowds of supporters and counter-protesters and escalating threats.

"The encampment had become increasingly untenable for the NYU community and the neighborhood we inhabit," she said.

Mills said three senior administrators spoke with the protesters over the weekend to come to an agreement over shutting down the encampment.

The president said things escalated on Wednesday when a group of people from a May Day march came to the walkway and got into altercations.

The May Day incident and other issues, including threats leveled at NYU administrators, led the school to call the NYPD, according to Mills.

"The university’s senior leadership and I were compelled to conclude that we could not tolerate the risk of violence any longer and that we could not responsibly or in good conscience wait until something drastically worse were to happen in order to act. We needed to bring this to a close," she said.