US police officers in helmets streamed into Columbia University on Wednesday evening to remove a group of mask-clad protesters who staged a pro-Palestinian demonstration inside the school's main library.

Videos shared on social media showed the long line of New York Police Department (NYPD) officers entering the library hours after dozens of protesters pushed their way past campus security officers, raced into the building, then hung Palestinian flags and other banners on bookshelves in an ornate reading room. Some protesters also appeared to have scrawled “Columbia will burn” across framed pictures.

Other videos showed campus security officers barring another group of protesters from entering the library, with both sides shoving to try and force the other group aside.

Videos showed more than 30 people being taken away from the library by officers with their hands tied behind their backs.

Protesters and other supporters, meanwhile, gathered around the metal barriers set up outside the building by police cheering on the detained demonstrators and chanting “Free Palestine”.

The university's acting president, Claire Shipman, said the protesters who had holed up inside a library reading room were asked repeatedly to show identification and to leave, but they refused.

The school then requested the NYPD come in “to assist in securing the building and the safety of our community”, she said.

Shipman said two university public safety officers sustained injuries as protesters forced their way into the building.

“These actions are outrageous,” she said, adding that the disruption came as students were studying and preparing for final exams.

New York City mayor Eric Adams said officers were entering the campus “to remove individuals who are trespassing”.

New York governor Kathy Hochul also denounced the protesters.

“Everyone has the right to peacefully protest,” the Democrat wrote on X. “But violence, vandalism or destruction of property are completely unacceptable.”

The demonstration and effort to break it up came the same evening that the Justice Department announced it had brought hate-crime charges against a man who had been repeatedly arrested at pro-Palestinian demonstrations over the past year, including one held near Columbia. An indictment charged Tarek Bazrouk, 20, with assaulting Jewish people at the demonstrations.

Columbia University in March announced sweeping policy changes related to protests following Trump administration threats to revoke its federal funding.

Among them are a ban on students wearing masks to conceal their identities and a rule that those protesting on campus must present their identification when asked. The school also said it had hired new public safety officers empowered to make arrests on campus.

Columbia University Apartheid Divest, a pro-Palestinian student group, said it had occupied part of Butler Library because it believed the university profited from “imperialist violence”. (AP)