Dozens of pro-Palestinian demonstrators were taken into police custody on Wednesday evening after occupying part of the main library on Columbia University’s campus in an attempt to rekindle the protest movement that swept the campus last spring.

The protesters, wearing masks and kaffiyehs, had burst through a security gate shortly after 3 p.m. and hung banners in the soaring main room of Butler Library’s second floor, renaming the space “the Basel Al-Araj Popular University,” according to the demonstrators and witnesses at the library.

Columbia security guards blocked them from leaving unless they showed their identification, causing an hourslong standoff. Outside the library, crowds gathered, leading to a chaotic scene. By about 7 p.m., Columbia administrators had called the New York City police back to campus for the first time since the occupation of Hamilton Hall, another campus building, in April 2024.

“Requesting the presence of the N.Y.P.D. is not the outcome we wanted, but it was absolutely necessary to secure the safety of our community,” Claire Shipman, the acting president of the university, wrote in a statement.

Ms. Shipman said that two public safety officers had been injured during a crowd surge outside the library, when some people had tried to force their way in. Several protesters also appeared to have been injured.