Michael R. Davidson, 37, was responsible for operating the fire hose nozzle for Engine Company 69, the first to arrive, the commissioner said. He was somehow separated from other firefighters when the blaze intensified and forced them to pull back from the building, officials said.

Image Firefighter Michael R. Davidson Credit... New York Fire Department

When he was found by other firefighters, he was unconscious, and critically injured. He was taken to Harlem Hospital, where he was pronounced dead.

“New York City is in mourning tonight,” Councilman Mark D. Levine said of Mr. Davidson in a tweet. “He made the ultimate sacrifice to save the lives of our neighbors. Horrific tragedy. We pray for his family and loved ones.”

Firefighter Davidson was a 15-year veteran of the Fire Department and had been cited for bravery four times, the department said. The names of the two injured firefighters, who were being treated for burns, were not released.

Commissioner Nigro said that fighting a fire in a cellar is one of the most dangerous tasks that firefighters take on, and that in a building that isn’t fireproof, like the one on St. Nicholas Avenue, flames are liable to spread rapidly. Several other firefighters had less serious injuries and three civilians received minor injuries, the commissioner said.