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.

Columbia University has distributed a letter to members of the encampment on campus telling them to gather their belongings and leave the area by 2 p.m., saying if they identify themselves and sign a form "to abide by all University policies through June 30, 2025, or the date of the conferral of your degree, whichever is earlier, you will be eligible to complete the semester in good standing."

The school said it has "already identified many students in the encampment" and "if you do not identify yourself upon leaving and sign the form now, you will not be eligible to sign and complete the semester in good standing." The school warned it could take action up to suspension or expulsion if they do not leave the encampment.

The school reiterated that negotiations with protesters had broken down and said the protests are a "disruption" to those taking final exams and preparing for graduation.

"As you are probably aware, the dialogue between the University and student leaders of the encampment is, regrettably, at an impasse," the letter states. "The current unauthorized encampment and disruption on Columbia University’s campus is creating an unwelcoming environment for members of our community. External actors have also contributed to this environment, especially around our gates, causing safety concerns – including for our neighbors."