At least 12 people have been arrested at the University of Wisconsin-Madison as campus police moved to disperse an encampment of protesters. About 100 to 200 people had arrived for a demonstration Monday and began putting up tents.

The University of Wisconsin said several people resisted arrest, but it is not yet clear how many of the arrested are affiliated with the university.

Several tents have been taken down and dissembled.

"Tents and camping are not allowed on any university property under Chapter 18 of the Wisconsin Administrative Code, which defines the types of activities permitted on campus, information which was shared to all members of the campus community on Friday," the university said in a statement.

The mayor said those who occupied Hamilton Hall were led by people unaffiliated with Columbia University.

Those protesters made a change to more aggressive tactics and represented an "elevated concern," Rebecca Weiner, the NYPD deputy commissioner of intelligence and counterterrorism, said Wednesday.

"The situation had deteriorated to the point where the safety of students, staff and the public was at risk," Police Commissioner Edward Caban said.

There were 282 arrests on a range of mainly minor offenses -- 173 at City College and 119 at Columbia.

"It was a tough decision," Adams said, of the university authorizing the NYPD to move onto campus. "The action had to end and we brought it to a peaceful conclusion."

-ABC News' Aaron Katersky

New York City Mayor Eric Adams and New York Police Department officials told reporters that protesters at Columbia University were being influenced by outside individuals, part of a movement "globally" to "radicalize young people"

"Students have a right to protest and free speech is the cornerstone of our society. But as our major concern we knew and we saw that there were those who were never concerned about free speech. They were concerned about chaos. It was about external actors hijacking peaceful protests influence students to escalate," Adams said.

"You don't have to be a majority to influence and co-opt an operation," Adams said.

About 300 people were arrested at Columbia University and City College Tuesday night, New York Mayor Eric Adams said Wednesday.

"We are processing the arrests to distinguish between who were actually students and who were not supposed to be on the grounds," Adams said.

"It was led by individuals who are not affiliated with the university. The school needed the NYPD assistance to clear Hamilton Hall at the encampments outside of dual operations on the grounds that took place successfully," Adams said.

Officials said those arrested could be charged with trespassing, criminal mischef and burglary.

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