New York Fire Commissioner Daniel Nigro said the Thursday fire that killed 12 people at an apartment in the Bronx was started by a three and a half year old boy playing with a stove.

Nigro told reporters Friday the boy’s mother fled the apartment with her son and other child, leaving the door open.  The fire then spread quickly, with the five story building's stairwell acting like a chimney.  Officials said housing records show the building had previous violations, including defective carbon monoxide and fire detectors.

Firefighters respond to a building fire, Dec. 28,
Firefighters respond to a building fire, Dec. 28, 2017, in the Bronx borough of New York. The Fire Department of New York says a blaze raging in the Bronx apartment building has left six people dead and more seriously injured.

Firefighters arrived on the scene in just over three minutes. Nigro called the loss of life from the fire, the worst in New York in 25 years, "unprecedented."

Authorities say about 170 firefighters battled the blaze and rescued the building's fleeing tenants.

Officials say at least four people were seriously injured in the fire, a block away for the world-renowned Bronx Zoo.

Bronx, New York