More than 160 firefighters responded to the blaze in the Bronx Thursday night.
The fire began around 7 p.m. in a building on Prospect Avenue, the New York Fire Department said. At least 15 people were treated for injuries.
Six people were killed, the New York mayor's office told the AP.
The fire was extinguished around 8:30 p.m., PIX 11 reported.
The fire broke as New York experiences frigid winter conditions, with temperatures dipping into the teens.
The Bronx was the scene of another deadly apartment fire in 2007, when nine children and one adult died in a blaze that officials said was caused by a space heater.
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