While the officers used no tear gas and said there were no injuries, they were forced to use flash-bang grenades to get past doors barricaded with chairs, tables and vending machines inside the building, the department told CNN.

Dozens of protesters were taken into custody, zip tied and escorted outside to NYPD buses. The rest of the campus was on lock-down, as students were ordered to stay inside their dorms.

Columbia University issued a statement Tuesday night, saying “the NYPD arrived on campus at the university’s request.”

“We believe the group that broke into and occupied the building were led by individuals who are not associated with the university,” Columbia administrators said, adding that they have requested NYPD to maintain a presence on campus through graduation, until May 17.

Earlier Tuesday, Columbia University warned the protesters, who entered and occupied Hamilton Hall after defying orders to vacate encampments, that they will face expulsion.

“We regret that protesters have chosen to escalate the situation through their actions,” Columbia wrote Tuesday in a communication to alumni, emailed to UPI.

“We made it very clear yesterday the work of the university cannot be endlessly interrupted by protesters who violate the rules. Continuing to do so will be met with clear consequences,” the university said.

“Protesters have chosen to escalate to an untenable situation — vandalizing property, breaking doors and windows, and blockading entrances — and we are following through with the consequences we outlined yesterday.”

Columbia University alumni demanded school officials end the occupation of Hamilton Hall “immediately” with the assistance of the NYPD and expel all students involved.

The takeover of Hamilton Hall “has crossed an indefensible line far beyond legitimate protest,” the Columbia Jewish Alumni Association wrote in a statement.

Late Tuesday afternoon, more protesters gathered on Amsterdam Avenue near the public safety checkpoint for the campus, chanting “Disclose, divest, we will not stop we will not rest,” as the presence of NYPD officers also grew.

“We’re in constant dialogue with the officials at Columbia University, so right now there is no timetable. We have no letters from them. We are here ready to assist them whenever they need our help,” NYPD Commissioner Edward Caban told reporters Tuesday afternoon.

New York City Mayor Eric Adams blamed “external actors” during the news conference, and called on protesters to “leave the area now.”

“They’re not here to promote peace or unity or allow a peaceful display of voice, but they’re here to create discord and divisiveness,” Adams told reporters, as he urged the parents of protesters to call their children and urge them to leave campus.

Protesters, occupying Hamilton Hall, unfurled a Palestinian flag outside the building earlier Tuesday and were seen getting crates of supplies from other organizers using a pulley system of ropes.

Education Secretary Miguel Cardona called the protesters’ behavior “abhorrent.”

“I think what’s happening on our campuses is abhorrent,” Cardona said Tuesday at the Senate’s budget requests hearing for fiscal year 2025. “It’s unacceptable and we’re committed as a Department of Education to adhering to Title VI enforcement.”

A steady stream of Columbia students were seen moving out of their dorms Tuesday, with Monday having been the last day of classes and final exams now remote due to the protests, while administrators warned people to stay away from campus.

“In light of the protest activity on campus, members of the university community who can avoid coming to the Morningside campus today should do so,” the university said in a public safety statement Tuesday morning. “Essential personnel should report to work according to university policy.”

Hamilton Hall stands in distinction for being taken over during campus anti-Vietnam demonstrations in 1968. Protesters came together outside of the building early Tuesday before a small group broke off and stormed the hall.

That group barricaded themselves inside using vending machines, chairs and the desk inside of Hamilton Hall. The demonstrators appeared to break windows from the inside as they were cheered on by the outside crowd.

The group Columbia University Apartheid Divest took responsibility for the Hamilton Hall storming on social media.

“This escalation represents the next generation of the 1968, 1985 and 1992 student movements which Columbia once repressed yet celebrate today,” the group’s message on X said. “Protesters have voiced their intention to remain at [Hamilton Hall] until Columbia concedes to CUAD’s three demands: divestment, financial transparency and amnesty.”

The occupation came hours after Columbia’s President Minouche Shafik said that talks had broken down between the university and protesting students by a deadline set for them to vacate encampments erected over Israel’s response to Hamas in Gaza since last October.

Columbia said it began suspending students who violated the deadline, barring them from entering university buildings and revoking their eligibility to complete the semester or graduate.

The protest at Columbia University is a part of protests at university campuses across the country protesting Israel’s action during the Gaza war that has left much of the region damaged and its residents desperate for humanitarian aid.