An under-construction high-rise in Manhattan was still unstable Tuesday after buckling columns and sagging floors raised fears of a collapse, forcing the tower and other nearby buildings to evacuate, officials said.

The 1970s-era office building is being converted to luxury apartments, and is the former global headquarters of pharmaceutical giant Pfizer. Initial reports of falling bricks at around 8 a.m. sent firefighters rushing to the busy corridor near Grand Central train station and the landmark Chrysler Building.

New York City officials were using drones to monitor the building to avoid having to send people inside. A nearby school that has 400 students was among the evacuated buildings, Mayor Zohran Mamdani said.

“The building remains unstable,” Mamdani said at a news conference at the scene. “This is an extremely serious situation.”

Fire Chief John Esposito said the way the steel-framed building is constructed, “it would not be a total collapse, it would be more of a localized collapse.”

Ahmed Tigani, the city’s building commissioner, said officials had not seen evidence that debris fell off the building. Nevertheless, nearby streets remained closed to people and vehicles. Mamdani said there were no reports of injuries.

The office-to-residential conversion would add more than a dozen stories and redesign an adjoining tower, according to Gensler, the architectural firm leading the project. With more than 1,600 units, it has been billed as the largest conversion in the city’s history, Gensler says.

A spokesperson for Gensler did not return a voicemail and email seeking comment.

Officials found two columns had buckled on the 21st and 22nd floors and floors were sagging between the 21st and 26th floors.

First responders and city officials were working closely with the project engineer to develop plans to shore up the impacted flooring, Mamdani said. If it’s deemed to be secure, engineers will enter and begin making repairs.

“This is a minute-by-minute assessment,” the mayor said.

The building commissioner said workers will need to add emergency beams and columns to stabilize the compromised ones.

“Our top priority right now,” the mayor said Tuesday morning, “is the safety of those who live in this area and the safety of those who work in this area.”