At least 25 people were arrested at CUNY's City College of New York campus as police confronted protesters early Wednesday, the university said in a statement.

University officials said they asked the New York Police Department for assistance in clearing protesters, including a "large crowd" of people who had marched from Columbia University to City College.

The school described a "series of violent indents" that it said put public safety at risk over the last six days.

"This includes a fire Sunday night at the Marshak Science Building caused by use of a flare gun that brought FDNY to campus, clashes with public safety, an attempted break-in at Shepard Hall tonight, and a break-in at the Administration Building tonight that included the vandalizing of offices and smashing glass doors," the university said in a press release early Wednesday.

Police entered the campus just before midnight and began making arrests, the university said.

"Students have a right to demonstrate peacefully and exercise their First Amendment rights," the university said. "Tonight's actions were taken in response to specific and repeated acts of violence and vandalism, not in response to peaceful protest"

-ABC News' Jessica Gorman and Kevin Shalvey

After Columbia University was cleared of encamped protesters Tuesday night, the school said it its Morningside campus was immediately restricted to students who live there and workers providing essential services.

"Effective immediately, access to the Morningside campus has been limited to students residing in residential buildings on campus (Carman, Furnald, John Jay, Hartley, Wallach, East Campus and Wien) and employees who provide essential services to campus buildings, labs and residential student life (for example, Dining, Public Safety, and building maintenance staff). There is no additional access to the Morningside campus," the notification read.

The university said the restrictions would stay in place "until circumstances allow otherwise."

-ABC News' Victoria Arancio

NYPD officers entered the campus of the City College of New York late Tuesday night.

"As requested by the university, we are currently on campus to assist the university in dispersing those trespassing," NYPD Deputy Commissioner of Operations, Kaz Daughtry, said in a post on X, sharing video of the police moving in.

In a note to the campus community, university president Vince Boudreau, said protests on campus presented "heightened challenges."

"Most importantly, this is not primarily a CCNY demonstration, and perhaps not primarily a CUNY demonstration. The significant inclusion of un-affiliated external individuals means that we don’t have established connections to them," Boudreau's letter read.

He continued: "Specifically, this demonstration has been more contentious and violent than anything we’ve seen on campus before. Today, we distributed a letter to members of the encampment detailing specific examples of threats to the safety of people within and outside the encampment, so that all of them understand the full scope of the activity. We also want all of them, and those of you reading this note, to understand that in no way does our response to this particular and extraordinary threat overwrite our more fundamental commitments to free speech, academic freedom, or the right to peacefully protest that comply with CCNY and CUNY regulations."

Boudreau said the encamped demonstrators were told to take down their encampment and follow CUNY guidelines for "future activities."

The university president also said classes would be remote on Wednesday due to the situation on campus.

-ABC News' Jolie Lash and Victoria Arancio

In a letter authorizing the NYPD to enter the Columbia University campus and break up the protest, the school detailed the backstory on its recent talks with those in the encampments and the takeover Tuesday night of Hamilton Hall.

According to the letter, from Columbia President Minouche Shafik, an individual "hid in the building" at Hamilton Hall until it was closed and let others in. The group's purpose was "occupying the building," the letter read.

Two security guards were inside the building at the time, and the university said in the letter to the NYPD they were able to "secure their release."

"We believe that while the group who broke into the building includes students, it is led by individuals who are not affiliated with the University," the letter read. "The individuals who have occupied Hamilton Hall have vandalized University property and are trespassing."
Addressing the encampment on the school's Morningside campus, the university told police discussions had been carried out with group representatives, but on Sunday, they "reached an impasse."

At that time, the university says it told the group they did not have permission to "occupy spaces on campus" and were "in violation" of school rules and policies.
On Monday morning, the protesters were told they would be suspended if they didn't disperse by Monday at 2 p.m. ET.

The university said in its Tuesday night NYPD letter that those in the encampment were "suspended" and "not authorized to be on University property and are trespassing."

The university said it believed the actions of those in the protest were escalating. "These activities have become a magnet for protesters outside our gates which creates significant risk to our campus and disrupts the ability of the University to continue normal operations," the letter read.

Columbia's president concluded the letter by asking the NYPD to "help to clear all individuals from Hamilton Hall and all campus encampments."

She further asked police to have a campus presence through May 17 -- graduation is May 15 -- "to maintain order and ensure encampments are not reestablished."

Police moved onto the Columbia University campus a little before 9 p.m. ET and began making arrests.

The NYPD also used a vehicle with an extendable roof ramp to help officers breach Hamilton Hall from an upper floor. From there, the police cleared the building.

The campus encampment and hall were cleared before 11:30 p.m.

-ABC News' Jolie Lash, Aaron Katersky and Joshua Hoyos

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