NEW YORK, Dec. 29 -- A devastating fire that killed 12 people and injured multiple others in a New York building was started by a small child playing with a stove burner, local authorities said on Friday.

New York City Fire Department Commissioner Daniel Nigro said the mother of the three-year-old boy was not aware of the fire until the child, who had been left unattended in the kitchen, started screaming as it filled with smoke and fire.

The mother exited her first-floor apartment with her two children, leaving the apartment door open, he said.

"The stairway acted like a chimney," Nigro said, adding that the fast-moving fire traveled up stairs and that people had very little time to react.

Some who tried to get back down the stairs had died, while others who went out through fire escapes were rescued by firefighters, he said.

Although firefighters arrived at the scene about three minutes after emergency calls came in and bravely entered the building to save residents, this blaze was "uNPRecedented," he added.

The fire broke out at round 7 p.m. at the five-story building in Bronx, the northernmost of the five boroughs of New York City.

Four children died along with four men and four women, local media reported.

New York City Mayor Bill de Blasio said at a press conference held late Thursday on the scene that the fire "will rank as one of the worst losses in a fire in many years."

De Blasio told reporters that four people remained in critical condition.

NEW YORK, Dec. 29 -- A devastating fire that killed 12 people and injured multiple others in a New York building was started by a small child playing with a stove burner, local authorities said on Friday.

New York City Fire Department Commissioner Daniel Nigro said the mother of the three-year-old boy was not aware of the fire until the child, who had been left unattended in the kitchen, started screaming as it filled with smoke and fire.

The mother exited her first-floor apartment with her two children, leaving the apartment door open, he said.

"The stairway acted like a chimney," Nigro said, adding that the fast-moving fire traveled up stairs and that people had very little time to react.

Some who tried to get back down the stairs had died, while others who went out through fire escapes were rescued by firefighters, he said.

Although firefighters arrived at the scene about three minutes after emergency calls came in and bravely entered the building to save residents, this blaze was "uNPRecedented," he added.

The fire broke out at round 7 p.m. at the five-story building in Bronx, the northernmost of the five boroughs of New York City.

Four children died along with four men and four women, local media reported.

New York City Mayor Bill de Blasio said at a press conference held late Thursday on the scene that the fire "will rank as one of the worst losses in a fire in many years."

De Blasio told reporters that four people remained in critical condition.