An officer accidentally discharged his gun as the New York Police Department worked to clear Hamilton Hall -- a building that had been occupied by Columbia University students on April 30, Assistant Chief Carlos Valdez, the commanding officer of the NYPD Emergency Service Unit, said Friday.

During the operation, a sergeant unintentionally discharged his firearm while attempting to gain access to an office.

"The sergeant was transitioning his firearm to his non-dominant hand to unlock the office door from the inside when the discharge occurred," Valdez said.

There were no injuries and the bullet was contained within the vacant office. Valdes said that at no point were police officers, members of the public or protesters in danger.

"This was purely unintentional," he said.

New York University and New School, in separate statements, said they requested police move students from their campuses after multiple rounds of negotiations failed.

NYU said the "encampment had become increasingly untenable for the NYU community and the neighborhood we inhabit." Classes will proceed as normal today.

NYU said it is aware of calls for a 4 p.m. protest at the former site of the encampment.

The New School, which switched to remote learning Friday, said students continued to set up in the lobby of the University Center building and block access to the "residence hall, classrooms, library, and cafeteria."

Despite the university "pleading to allow their fellow students to enter their residence hall, the protesters would not budge."

The New School said the protests continued even after they "provided a confirmed date this month for the Investment Committee to consider a vote on disinvestment."

"It is a sad day for all of us who are part of this university community and who believe in free speech, which we have pledged to protect and will continue to protect," The New School said in a statement.

Fifty-six people have been arrested at The New School and New York University after the schools authorized police to clear encampments, according to the New York Police Department.

Forty-three people were arrested at The New School and 13 people where arrested at NYU, the NYPD said.

-ABC News' Aaron Katersky

NYU has requested assistance from the NYPD to "disperse the illegal encampment on their property."

"As per their request, we are on site and our officers will be assisting with the unparalleled professionalism embodied by our police officers," NYPD Deputy Commissioner, Operations Kaz Daughtry, said in a statement on social media.

In a letter authorizing the NYPD to enter the Columbia University campus and break up the protest, the school detailed the backstory on its recent talks with those in the encampments and the takeover Tuesday night of Hamilton Hall.

According to the letter, from Columbia President Minouche Shafik, an individual "hid in the building" at Hamilton Hall until it was closed and let others in. The group's purpose was "occupying the building," the letter read.

Two security guards were inside the building at the time, and the university said in the letter to the NYPD they were able to "secure their release."

"We believe that while the group who broke into the building includes students, it is led by individuals who are not affiliated with the University," the letter read. "The individuals who have occupied Hamilton Hall have vandalized University property and are trespassing."
Addressing the encampment on the school's Morningside campus, the university told police discussions had been carried out with group representatives, but on Sunday, they "reached an impasse."

At that time, the university says it told the group they did not have permission to "occupy spaces on campus" and were "in violation" of school rules and policies.
On Monday morning, the protesters were told they would be suspended if they didn't disperse by Monday at 2 p.m. ET.

The university said in its Tuesday night NYPD letter that those in the encampment were "suspended" and "not authorized to be on University property and are trespassing."

The university said it believed the actions of those in the protest were escalating. "These activities have become a magnet for protesters outside our gates which creates significant risk to our campus and disrupts the ability of the University to continue normal operations," the letter read.

Columbia's president concluded the letter by asking the NYPD to "help to clear all individuals from Hamilton Hall and all campus encampments."

She further asked police to have a campus presence through May 17 -- graduation is May 15 -- "to maintain order and ensure encampments are not reestablished."

Police moved onto the Columbia University campus a little before 9 p.m. ET and began making arrests.

The NYPD also used a vehicle with an extendable roof ramp to help officers breach Hamilton Hall from an upper floor. From there, the police cleared the building.

The campus encampment and hall were cleared before 11:30 p.m.

-ABC News' Jolie Lash, Aaron Katersky and Joshua Hoyos