Several Midtown Manhattan blocks were evacuated Tuesday morning after construction workers discovered the structure of a massive office building being converted into residential housing was compromised on the 21 st floor,

The structure, which is under construction, was evacuated along with surrounding buildings after reports of falling bricks.

The complex, which once housed offices for the pharmaceutical company Pfizer, is being converted to residences. Officials inspecting it found that support columns were buckling and upper floors were sagging.

At that point, you need to add more steel -- and they obviously didn’t add the right amount of steel,” Johnsen said.

Authorities evacuated a Manhattan office building after construction workers observed multiple floors collapsing and bricks falling from the facade.

Video from inside a New York City high-rise under renovation showed multiple buckling beams. The former Pfizer building is being renovated from an office into residential apartments.

Steel support columns in the Midtown building, which is being converted from offices into apartments, may have been overloaded, experts say

Photos show buckling beams and sagging floors at NYC high-rise on the verge of collapse -