Death toll and injuries may rise, press secretary for the New York Mayor says.
The blaze broke out in a five-story building's third floor and quickly spread near the Bronx Zoo and a college.
Eric Phillips, press secretary for New York's Mayor Bill de Blasio, said there were 12 fatalities but the death toll was still uncertain and it may rise.
"Will be more. Horrible. Fire Commissioner on scene. Mayor here shortly,” Phillips wrote in a tweet.
Mayor de Blasio, en route to the scene, is expected to speak at a press conference.
New York City Fire Department (FDNY) said more than 160 firefighters were on the scene and battling the flames in bone-chilling cold, -9 celsius degrees, to rescue people from the building and the fire is not yet under control.
The victims reported injured were in either serious or critical condition and were taken to nearby Medical Centers, according to the FDNY.
The American Red Cross Greater New York arrived on the scene, and were giving out blankets to the rescued people who were stuck without access to their apartments.
Further details on the incident were not immediately available.