A fast-moving four-alarm fire ripped through the roof of a six-story apartment building in Claremont on Friday afternoon — and led firefighters to a gruesome discovery on the same floor where the flames began.

Fire officials said a body was found inside a sixth-floor apartment. The NYPD said the discovery is unrelated to the fire but has launched a separate investigation into the death.

The fire broke out just after 3 p.m. on Sheridan Avenue, sending heavy smoke through the building and forcing dozens of residents to flee.

“I was in the living room with my mom," said Joseph, a first-floor tenant. "We were just watching TV and an officer comes knocking on our door yelling ‘fire, fire.'"

Joseph said he only had time to grab his dog — still shaking from the chaos — before running into the street.

The FDNY said more than 170 firefighters responded within four minutes, battling the flames amid a high wind advisory. Crews broke through the ceiling inside apartment 6H and cut open the roof to keep the fire from spreading.

“The fire was in that air. We had to open up the ceilings from below and also from above. We had to cut the roof away to fully extinguish the fire in that area,” Division Chief John Nevins said.

Nine people were hospitalized, including three firefighters and four police officers. Nevins said those officers ran through smoke-filled hallways to get residents to safety.

City records show the building has 66 violations with the Department of Buildings, including a partial vacate order for “hazardous conditions.”

The cause of the fire remains under investigation. Police have not yet released the name of the person found dead.