A Manhattan high-rise remained unstable Tuesday after structural columns buckled and floors sagged during work to convert the former Pfizer headquarters into luxury apartments, forcing evacuations and major street closures in Midtown.

The building, located at 235 East 42nd Street between Second and Third Avenues, is an active construction site being converted from commercial office space into residential use. Officials said structural issues were found on the 21st floor, where two columns buckled and multiple cracks and sagging floors were discovered.

Mayor Zohran Mamdani called the situation “extremely serious,” saying first responders and structural engineers were working with the project engineer to develop a plan to shore up the impacted floor.

“This is a minute-by-minute assessment,” Mamdani told reporters near the scene.

Fire officials said the damage spans floors 21 through 26, with continued movement detected in one of the compromised columns after emergency crews arrived. FDNY Chief John Esposito said specialized monitoring equipment was being used to detect even small shifts in the structure.

“It does mean that it is not yet stable. It is still a very serious and dangerous situation,” Esposito said.

Esposito said the building’s steel-frame construction makes a total collapse unlikely, but warned that a localized collapse remains possible.

“It would not be a total collapse, it would be more of a localized collapse,” he said.

At least nine nearby buildings were evacuated as a precaution, including a school with roughly 400 children inside and the Israeli Consulate across the street. A nearby hotel was also reportedly evacuated.

The NYPD established a frozen zone from 40th to 45th Streets between First and Third Avenues, closing the area to both pedestrians and vehicles while engineers and emergency crews assessed the building.

Officials said there were no injuries and that all workers at the construction site had been accounted for.

The project is described by developers as the largest office-to-residential conversion in New York City history, with more than 1,600 units planned. Buildings Department records show the project has previously been fined for multiple safety violations, including falling glass and metal, as well as an incident involving a worker falling from a ladder.

The Department of Buildings said workers will need to install emergency beams and columns to stabilize the compromised areas before repairs can proceed.

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