Citizen App video shows firefighters responding to the scene on Third Avenue near East 38th and 39th Street around 6:30 a.m. on Sunday.
The FDNY says about 60 fire and EMS personnel helped battle the fire. Police also responded to the scene, and upon arrival, officers were informed that a 40-year-old man was discovered unconscious inside the building.
First responders transported the victim in critical condition to Bellevue Hospital, where he was later pronounced dead.
Fire marshals are trying to determine the cause of the blaze.
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