“People died on various floors of the apartment, ranging in age from 1 to over 50,” city Fire Commissioner Daniel Nigro told reporters at a news conference with the mayor.
“This tragedy is without question historic in its magnitude.”
In a message to New Yorkers, de Blasio said, “Hold your families close and keep those families here in the Bronx in your prayers.”
Few official details of the blaze were immediately available. WABC-TV, the New York affiliate of the ABC television network, said it erupted shortly before 7 p.m. on the third floor of a five-story building.
There was no serious damage to the exterior of the building visible in news footage and images from the scene.
The New York City Fire Department initially had said on its Twitter account that 15 serious injuries to civilians were reported in the four-alarm blaze, and that more than 160 firefighters were on the scene.
Photographs posted on Twitter by the fire department showed two fire trucks with ladders extended to the upper floors of a brick building bathed in flood lights, and firefighters on the fire escape outside what appeared to be a second- or third-floor unit.
The mayor’s official Twitter page displayed a photo of de Blasio, standing in the room of a school across the street from the fire , with his hands on his hips and a grim look on his face as he was being briefed by fire authorities before speaking to reporters.
A fire tore through a Bronx apartment building on Thursday, killing at least 12 people, including a toddler, and leaving four others fighting for their lives in New York's deadliest blaze in decades.
The fire broke out around 6:51pm (2351 GMT) in a 25-apartment building near the Bronx Zoo, one of the most popular tourist attractions in the US financial capital.
A one-year-old child was among those killed as Red Cross volunteers handed out blankets and emergency responders set up a makeshift shelter in a nearby school on a bitterly cold night.
Tearful residents spoke of hearing shouts of “fire, fire” in the building and a mad rush to exit the property, battling past the smoke, with just the clothes on their backs into the sub-freezing night.
Mayor Bill de Blasio called it an “unspeakable tragedy,” in the middle of the holiday season when families come together, as the city of 8.5 million straddles Christmas and New Year festivities.
“Tonight here in the Bronx there are families that have been torn apart.
This is the worst fire tragedy we have seen in this city in at least a quarter century,” de Blasio said.
“I am sorry to report 12 New Yorkers are dead, including one child as young as one year old,” he told reporters after fire fighters extinguished the flames.
“There are four people critically injured who are fighting for their lives, other serious injuries as well,” he added.
The blaze began on the first floor and spread rapidly throughout the five-floor walk-up on Prospect Avenue, with fire fighters on the scene within three minutes, department chief Daniel Nigro told reporters.
'Died on various floors'
Television footage showed fire fighters plucking panicked residents to safety from a fire escape.
Two of the dead were discovered in a bath tub full of water, where they had apparently sheltered from the blaze, US media reported.
Nigro said it was “way too early” to comment on the cause of the inferno.
At least 12 people were rescued, but the search of the building continues, and the death toll could rise further, the mayor warned.
“This tragedy is, without question, historic in its magnitude. Our hearts go out to every family who lost a loved one here and everyone fighting for their lives,” said Nigro.
“People died on various floors, they range in ages from one to over 50,” he added.
“In a department that's certainly no stranger to tragedy, we're shocked at this loss.” It was the second deadly New York residential blaze in less than two weeks.
A mother and three children were killed in Sheepshead Bay, Brooklyn when a fire tore through their home on December 18.
In March 2007, 10 people were killed in another fire in the Bronx that tore through a home to two immigrant families, itself the worst fire in the city since 1990 apart from the September 11, 2001 attacks.
The New York Times said on Thursday's blaze was the worst in the city since 87 people were killed in a 1990 inferno at a Bronx social club.
