Dramatic video from inside the former Pfizer headquarters tower in Midtown Manhattan shows large I-beams buckling, and officials are warning of a possible collapse.

The 33-story high-rise at 235 East 42nd Street is undergoing a major office-to-residential conversion, one of the largest projects of its kind in the New York City metro area.

Local media outlet Pix 11 cited the FDNY, which said floors 21 through 26 have caved in, and major cracks and sagging floors were seen throughout the tower.

A union member working on the site told local media that workers allegedly failed to add sufficient steel support columns to handle the additional load from a new structure being built atop the original building.

"What happened here is that this building was renovated. They were going to add another 16 stories to it. But at that point you need to add more steel. And obviously they did not add the right amount of steel - so the north side of the building is crumbling. The I-beams are bending like cigarettes," the union member said

The New York Times reported that the building is being converted by Metro Loft into a residential tower with more than 1,600 apartments. Architects have described it as the largest project of its kind in NYC history, and it is scheduled to be completed in 2027.

The former Pfizer tower is part of a larger push to convert underused Midtown office space into residential units as NYC seeks to ease its housing shortage.