NEW YORK (CBSNewYork) — Twelve people were killed in an extra-alarm fire in an apartment building in the Belmont section of the Bronx, Mayor Bill de Blasio said late Thursday.

“In the middle of the holiday seasons – a time when families are together – tonight here in the Bronx, there are families that have been torn apart,” de Blasio said.

De Blasio said at a news conference at the scene that four people were also in critical condition and fighting for their lives late Thursday. There were other serious injuries as well, de Blasio said.

The figures were based on preliminary information that will be updated, de Blasio said.

The patients were taken to St. Barnabas Hospital and NYC Health + Hospitals/Jacobi.

“This is the worst fire tragedy we have seen in this city in at least a quarter century,” de Blasio said. “Based on the information we have now, this will rank as one of the worst losses of life to a fire in many, many years.”

PHOTOS: 12 Dead In Bronx Fire

The fire broke out on the first floor of a five-story building with 25 apartments at 2363 Prospect Ave., at East 185th Street just west of Bronx Park and the Bronx Zoo. The FDNY was called to the scene at 6:51 p.m. and arrived at 6:57 p.m., Fire Commissioner Daniel Nigro said.

The blaze was raised to three alarms and later to four, and the fire quickly spread upstairs through the building, Nigro said. And despite the best efforts of firefighters to revive those at the scene, it was too late.

Nigro said the people who died were on various floors of the building. He said the victims who died ranged in age from 1 to 50.

De Blasio said 12 others were rescued and will survive. But the search of the building continued late Thursday, and the mayor said, “We may lose others as well.”

About 170 firefighters responded to the scene, and were up against extreme cold as they fought the blaze. Temperatures were in the high teens Thursday night, with wind chills in the single digits.

Nigro said it was much too early to talk about any possible cause.

“As of now, this tragedy is without question historic in its magnitude here, and our hearts go out to every family that lost a loved one here, and everyone that’s fighting for their lives,” Nigro said.

CBS2’s Valerie Castro talked with one man who lives across the street from the building that caught fire.

“All I saw was just kids in the fire escape with their property, you know what I mean? And the flames were still going as the kids were, you know, on the fire escape,” said witness Rafael Gonzalez. “What woke me up was the smoke, because I thought it was my building.”

Kimberly Wilkins is a next-door neighbor.

“The fire truck wasn’t even here yet when all the smoke was coming out at first. They weren’t even here yet. They started to get everybody out, but people were up on the fire escape already trying to get down on their own,” she told 1010 WINS’ Andrew Falzon. “That’s how fast it was moving. People were screaming: ‘Fire! Help! Help!’”

As CBS2’s Elise Finch reported, as of 6 p.m., it was 13 degrees in the Belmont section of the Bronx when the fire broke out just before 7 p.m., with winds at 21 mph and a wind chill of 1 below zero.

By 10 p.m., the temperature had dropped to 10 degrees with winds still at 21 mph and a wind chill of 4 below zero.

But in order to save their own lives, full families were seen racing out of the burning building – some wearing only T-shirts, and some children wearing no shoes.

The American Red Cross Greater New York responded to the scene, and were giving out blankets to evacuees and people who were stuck without access to their apartments.

Office of Emergency Management Commissioner Joe Esposito said a nearby school, Crotona International Academy, 2474 Crotona Ave., had been opened as a reception center for those displaced.

De Blasio said in a final remark, “Everyone this evening, hold your families close and keep the families here in the Bronx in your prayers.”