As smoke and flames flew out of the seventh floor of an apartment building, debris fell from the crumbling facade.

Neighbors, like Gopal Krishna, reported hearing a loud boom before the fire broke out.

“I heard the sound. And it sounds like kind of blast,” said Krishna.

Fire department officials say they found evidence of an explosion on the top floor of the building on 41st Avenue in Elmhurst just before 10:30 a.m. Tuesday morning.

“We have significant damage to the penthouse structure, as well as the rear of the sixth floor. We have a collapse. It is a very unstable situation right now,” said FDNY Chief Thomas Currao.

One resident was killed. Four firefighters suffered minor injuries while battling the blaze. Some building residents, like Melissa Goldstein, were already at work at the time of the explosion. 

“I’m on a high floor and I have pets in the building. And I have no idea what their fate is right now and it’s killing me,” said Goldstein.

The Red Cross is assisting displaced tenants. Adjacent buildings were also evacuated. 

Department of Buildings inspectors and engineers are investigating the stability of the top level of the building.

Fire officials said the cause of the explosion is still under investigation.