Update 12/29, 10:30 a.m. ET: Officials believe they have discovered the cause of a deadly fire that swept through a Bronx apartment building. Mayor Bill de Blasio announced Friday that it appears that the fire started with a child playing with a stove on the first floor, The Associated Press reported.

Among the victims of the fast-moving fire were three girls aged 1, 2 and 7 and a boy whose age was not released, The AP reported.

Original post: A massive apartment fire in the Bronx in New York has left at least 12 people dead, including four children, and others seriously injured, according to New York Mayor Bill de Blasio's office.

Calling it one of the “worst fire tragedies we have seen in this city in a quarter century,” de Blasio said “it will rank as one of the worst losses in a fire in many years.”

Officials said the fire is the most deadly in New York City since 87 people died in the Happy Land arson attack on March 25, 1990, The New York Post reported. That blaze, which occurred at a social club, was located less than a mile away  from Thursday night's fire.

De Blasio said four people are in critical condition and 12 people were rescued as firefighters continue searching the building.

“We may lose others as well,” he said.

Five people perished inside the five-story, 25-apartment building and seven died at two hospitals, The New York Daily News reported.

Firefighters respond to a deadly fire Thursday, Dec. 28, 2017, in the Bronx borough of New York. The New York City mayor's press secretary says several people have died in the blaze on a frigid night, and several more have been injured.

Credit: Frank Franklin II

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Credit: Frank Franklin II

Firefighters were called to the scene of the fire just before 7 p.m. Thursday night near Fordham University and the Bronx Zoo on a bitterly cold night as flames spread through the building, according to The New York Times. At least 160 firefighters converged on the scene to help battle the flames.

“We’re shocked by this loss,” New York Fire Department Commissioner Daniel Nigro said.

“The fire started on the first floor, quickly spread upstairs into this … five-story building with 25 apartments,” Nigro said. “People died on various floors of the apartment. We won’t tell you anything more about it other than they range in ages from 1 to over 50.”

Among the missing is a U.S. Army soldier, the Daily News reported.

Kwabena Mensah, 62, said his 28-year-old son, Emmanuel, was home for the holidays. Mensah said his son’s roommate last saw him when the fire broke out on the third floor.

“He was telling the roommate to not come out of the apartment because there was smoke. But when they rescued everyone from the windows, we couldn’t find him. I went to four hospitals, I can’t find him,” Mensah told the Daily News.

At St. Barnabas Hospital, Brian Whittaker, 36, was lending his support to an injured friend’s relatives.

“It's such a tragedy because they lost so many family members,” Whittaker told the Daily News. “The rest of the family is upstairs in the back. They keep passing out and crying. The father is burnt up real bad.”

Whittaker’s friend was badly burned and is in a coma at Jacobi Medical Center. The man’s daughter and three nieces were killed, Whittaker told the Daily News.

“They were on the fifth floor so they weren't able to make it,” Whitaker said. “Who knows how intense the heat was? I saw it on the news and got a call from a bunch of friends. We came over here around midnight and been here since.”

Firefighters leave after putting out a major house fire in the Bronx borough of New York City.

Credit: Amir Levy

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Credit: Amir Levy

Thierme Diallo fled the building in a panic, awoken by a neighbor, the Daily News reported.

"Someone knocked on my door yelling 'Fire! fire! fire!’ I left my cellphone,” she said. “I took only my wallet because I need to save myself."

Luc Hernandez, a fourth-floor resident, said she came home about 15 minutes after the fire began and “saw black smoke everywhere.”

Hernandez said she rushed into her apartment, grabbed her 11- and 7-year-old boys and scrambled down the fire escape.

A second-floor resident named Rafael said he barely escaped.

“The smoke was bad. I had to run for my life out of there,” he told the Post.

Milka Garcia, who lives on the fifth floor of the building, said she came home to find her three children had been evacuated.

She said her 10-year-old daughter went to school with one of the victims, who’s about 8 years old, at Public School 205.

“This is horrible,” Garcia told the Daily News. “It makes me sad because they were my neighbors, and friends of my daughter’s.”

Not including the 9/11 terror attacks, the worst fire in New York City history was the Brooklyn Theater fire of Dec. 5, 1876, which claimed at least 278 lives, the Post reported.

The only other city fire more deadly than the Happy Land arson blaze was the Triangle Shirtwaist Factory fire of March 25, 1911.

“We're all struggling with unanswered questions and broken hearts,” Bronx Borough President Ruben Diaz Jr. said.