Entire blocks have been evacuated in New York City amid fears for the potential collapse of an under-construction skyscraper.

Columns in the 37-level Manhattan high-rise buckled and bricks tumbled into the street below during Tuesday morning’s hour, forcing the evacuation of nearby buildings.

“It’s a very serious situation because the box beams – the steel beams – have started to bend and deflect from the weight,” New York Fire Department chief Esposito said.

“We evacuated the building and started evacuations of surrounding buildings. The building has continued to move since we have been on the scene.”

The high-rise – once home to global pharmaceutical giant Pfizer – is being converted into luxury apartments. It is located in a busy corridor about a block from the landmark Chrysler Building and between Grand Central Terminal and the United Nations headquarters.

The fire department sent in drones, finding that there were serious structural issues on the 21st floor. Two structural columns have buckled, and there are multiple cracks and sagging floors from the 21st to 26th levels.

“We have specialised tools that we can watch the building from and see movement, even in centimetres or fractions of an inch. And since we arrived on the scene and put that in place, we have seen continual movement,” Esposito said.

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

The department said all workers had been accounted for by Tuesday afternoon (local time).

New York City Mayor Zohran Mamdani said a nearby school with about 400 children was among the buildings evacuated.

A Chicago family in NYC for last week’s July 4 celebrations were among people evacuated from hotels in the area.

“We were on the 21st floor — so sprinting down the stairs, and they said evacuated over to 2nd Avenue. All of our bags, and laptop bag and work bag, is back up at the hotel room,” Kevin Oglesbee said outside the evacuation zone.

“We’re supposed to leave for the airport in a few hours.”

British tourist Atish Parmar, who is visiting the city with his daughters, said they learned of the emergency evacuation only when they returned from a Central Park bike ride.

“We were just having lunch and we seen it all over the news, and we’re like, ‘Hang on, that’s our — that’s the same place’,” Parmar told CNN.

“Of course, we’re concerned about it. Thankfully, no one’s in there, but my daughter was a bit anxious.”

There is not yet any time frame for people returning to the evacuation zone.

There were later reports that contractors had been told to go ahead with installing temporary shoring on the building.

Mamdani said engineers were working on ways to shore up the damaged floors. He described the situation as “extremely serious”.

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

The office-to-residential conversion of the 1970s tower has been billed as the largest in New York City’s history, according to Gensler, the architectural firm behind it. The planned complex will have more than 1600 units and includes adding more than a dozen levels to the original tower, as well as redesigning an adjoining tower.

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