Fire investigators say a child playing with a stove is the cause of Thursday's massive five-alarm fire in the Bronx that left at least 12 people dead.

Four others remain in critical condition.

The New York City Fire Department says the flames broke out on the first floor of a five story building around 7 p.m. Thursday on 2363 Prospect Avenue in Belmont.

Fire Commissioner Daniel Nigro says their preliminary investigation found that a 3-year-old child was playing with the burners on the stove unsupervised.

The commissioner says the mother was alerted to the fire when the boy started screaming. He says she then exited the apartment with the 3-year-old and a 2-year-old but left the apartment door open. He says that decision caused the fire to quickly spread up the stairwell "like a chimney" to the above floors.

The FDNY says it took crews three minutes to arrive on the scene.

Some residents who were able to make it to the fire escape were rescued by firefighters while others perished as they tried exiting the smoke-filled stairs inside.

"This loss is unprecedented. It is the time of year where people celebrate and certainly here we have people who lost their lives, lost their homes, lost everything. And we grieve with them as everyone in this city should and does," Nigro said.

A 1-year-old child is the youngest death - the oldest is a 63-year-old woman.

Four of the victims have been identified as Karen Stewart, 37, Kelly Francis, 6, Kiley Francis, 2, and Shante Francis, 19.

Officials say it's the city's deadliest fire - excluding the September 11th attacks - since the Happy Land nightclub fire that killed 87 people in 1990.

Nearly 200 firefighters battled the blaze at the five-story, walk-up building that houses roughly 25 apartments.

Temperatures in the teens with wind chill in single digits added to the difficulty of their battle.

Thursday's deadly fire is reminiscent of a similarly devastating one from 2007.

That fire that took the lives of ten Malians who were living in the Highbridge neighborhood of the Bronx.

Nine of the victims were children, and five of those kids were from the same parents.