A school spokesperson says the NYPD began moving onto the campus around 9 p.m. at the university's request, saying the decision was "made to restore safety and order to our community."
WATCH | Eyewitness News coverage as NYPD moves in on Columbia campus
NYPD begins arresting protesters on campus at Columbia University
In its statement, the university said after they learned protesters had entered Hamilton Hall and "occupied, vandalized, and blockaded" it, they were left with "no choice" but to allow the police in. The university also said in a statement that they believe "that the group that broke into and occupied the building is led by individuals who are not affiliated with the University."
The university said in its statement the NYPD's presence is about the "actions of the protestors, not the cause they are championing."
Officers could be seen climbing a ladder and entering the building through a second-floor window of Hamilton Hall.
New details about how the NYPD entered Columbia's campus
Authorities say no tear gas was used inside the building, but they used four so-called "flash bang" grenades, which makes a loud noise.
About 50 arrests were made inside the building, according to police sources. Authorities say the first round of arrests came from inside the building and the surrounding area.
Police sources say most of the protesters arrested were not Columbia students, but rather "mostly professionals."
Hours after police moved in, the Columbia's Hamilton Hall and the encampment were cleared out, leaving just the tents which the school will clear. There were no reported injuries during the operation.
In a statement from Columbia, the school said only students who live in residential halls directly on the Morningside campus will be allowed on the campus grounds, along with employees who provide essential services to the main campus.
The major development came after a shelter-in-place order was issued to students as police activity around campus grew more intense Tuesday night. The message, issued to students, asked them to "shelter in place for your safety due to heightened activity on Morningside campus." The message went on to say that "non-compliance may result in disciplinary action."
Before officers stormed the campus, police gathered outside the school setting up barricades next to the campus.
The escalation in police activity came after dozens of pro-Palestinian protesters entered the school and occupied Hamilton Hall early Tuesday.
Video footage showed protesters on Columbia's Manhattan campus locking arms in front of Hamilton Hall and carrying furniture and metal barricades to the building after smashing through part of a glass door.
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The school said in a statement that those protesters will face expulsion.
"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," the school's statement said.
Mayor Eric Adams, alongside NYPD officials on Tuesday evening, said they "cannot wait till this situation becomes even more serious. This must end now."
Mayor Adams, NYPD officials hold update on situation at Columbia
"Over the past few weeks, we have observed that the protests have been co-opted by professional outside agitators," Mayor Adams said. "These individuals are not affiliated with Columbia and are creating serious public safety issues."
NYPD Commissioner Edward Caban and Deputy Commissioner for Intel, Rebecca Weiner, outlined the NYPD's observations of increased disruptive tactics, including individuals in black bloc attire, barricading, and property destruction.
"These once peaceful protests are being exploited," Commissioner Caban said.
In a demonstration of the unrest, a two-minute video was shown, narrated by the commissioner, highlighting the aggressive tactics and the involvement of external individuals who, according to him, are not affiliated with the university. The footage showed protestors and external actors fortifying entry points into Hamilton Hall.
Ben Chang, Columbia's Vice President of Office of Public Affairs, noted the protesters in Hamilton hall numbered in the dozens, and there were dozens more on the south lawn. He compared that to the student population of 37,000, and 15,000 who will be graduating May 15.
A graduate student who represents the student coalition that ran the main encampment said she believed up to 60 protesters were inside Hamilton Hall.
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The building was likely chosen because of its significance as it has been the center of campus protests and seized throughout history. It was one of several that was occupied during a 1968 Civil Rights and anti-Vietnam War protest on the campus.
WATCH | Professor looks back at Columbia University's Civil Rights, anti-Vietnam War protests of 1968:
Professor looks back at Columbia University's Civil Rights, anti-Vietnam War protests of 1968
Chang said the school had been negotiating with student protesters in good faith and these new measures are in place to ensure a smooth commencement on the quad in just two weeks.
"We also do not want to deprive thousands of students and their families and friends of a graduation celebration. Please recall that many in this graduating class did not get a celebration when graduating from high school because of the pandemic, and many of them are the first in their families to earn a University degree. We owe it to all of our graduates and their loved ones to honor their achievement," Columbia University President Dr. Minouche Shafik said.
"The university has conducted itself with obstinacy and arrogance, refusing to be flexible on some of our most basic points," protester Sueda Polat said. She said the students would return to the table if Columbia were willing to discuss divestment from Israel.
Earlier Monday morning, in a letter from Shafik, the school said it would not divest from Israel, rejecting the student protesters' "priority demand." The university acknowledged the pain the encampment has caused, especially for Jewish students.
"I know that many of our Jewish students, and other students as well, have found the atmosphere intolerable in recent weeks. Many have left campus, and that is a tragedy," the statement said. "To those students and their families, I want to say to you clearly: You are a valued part of the Columbia community. This is your campus too. We are committed to making Columbia safe for everyone, and to ensuring that you feel welcome and valued."
Meanwhile, tensions boiled over at the City College of New York where the NYPD also moved in and arrested demonstrators Tuesday night.
NYPD making arrests at City College of New York
In a emergency message to the college community, City College President Vince Boudreau announced as of May 1, all campus operations would be online until further notice.
"Given the situation, we are moving all Wednesday classes and work to remote, remaining remote until conditions permit a return to normal business operations. We are also urging all members of our community to stay away from campus," Boudreau said.
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Key moments over the last week at Columbia University
There has been growing criticism of Columbia's handling of pro-Palestinian demonstrations on campus, including the administration asking the NYPD to come in and clear protesters, resulting in more than 100 arrests earlier this month.
By a vote of 62-14, Columbia's Faculty Senate on Friday voted overwhelmingly in favor to investigate the school's leadership, led by President Minouche Shafik.
The 13-member executive committee shared a report that cited many actions and decisions that it believes have harmed the institution. Notably, the committee was unanimously against bringing the NYPD on campus to clear protesters from their encampment last Thursday, but Shafik did so anyway.
It marked a significant - but largely symbolic - rebuke from faculty Friday, but Shafik retained the support of trustees, who have the power to hire or fire the president.
The votes came as Columbia banned a student protest leader from campus for incendiary comments he made back in January.
In a video that recently resurfaced, Khymani James, a student activist associated with the Columbia University Apartheid Divest (CUAD) coalition, made the comment that "Zionists don't deserve to live."
In an interview with Bill Ritter for Up Close, New York City Mayor Eric Adams called the college protests unprecedented. Adams said during the interview that he believes outside agitators are behind the demonstrations.
"I have never witnessed the type of hateful, harmful and painful terminology that we're witnessing right now. I cannot recall any time in the period of protesting that we called for the eradication or extinction of any particular group," Adams said.
ALSO WATCH | Mayor Adams addresses unrest on NYC college campuses:
Extra Time: Mayor Adams addresses unrest on NYC college campuses
The Associated Press contributed to this report.
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