Nineteen people, including nine children, were killed on Sunday when an apartment fire started by a malfunctioning space heater sent smoke billowing through a Bronx high-rise, officials said, in the deadliest fire New York City had seen in more than three decades.

An additional 44 people were injured, 13 of them critically, after the occupants of the third-floor apartment where the fire started fled without closing the door behind them, the fire commissioner, Daniel A. Nigro said at a news conference at the scene.

“Smoke spread throughout the building, thus the tremendous loss of life and other people fighting for their lives,” he said.

The smoke from the fire spread to the top of the 19-storey building, darkening hallways and stairwells and shocking residents who had heard the fire alarms but did not immediately react because they had grown accustomed to frequent alarms in the building.

Firefighters found victims on every floor and worked to rescue them even as their own oxygen tanks ran low, Commissioner Nigro said.

Dana Campbell was summoned home by her four children when smoke began seeping into their apartment. She arrived as they leapt out of a third-floor window onto a makeshift landing pad, and was relieved to see they were not harmed.

“You can be here tomorrow with broken legs,” she said. “You can’t be here tomorrow with smoke inhalation.”

The fire’s toll was the worst in the city since 87 people died in an intentionally set fire at a Bronx nightclub in 1990 and was an early test for the city’s new mayor, Eric Adams. “The numbers are horrific,” Adams said.

He vowed that the city would provide support for the victims, many of whom are Muslim immigrants from the West African nation of Gambia.

Thirty people remained in the hospital on Sunday evening, Adams said. He urged all of the injured and displaced victims to seek help and assured those who may be undocumented that their information would not be passed along to federal immigration authorities.

A city official, who spoke on the condition of anonymity because the fire was still under investigation, said fire marshals believe the space heater had been running for several days uninterrupted. The residents were using the heater to supplement the building’s heat, which was on.

Apartment doors left open during fires have featured in some of the city’s worst blazes, including a Bronx fire in 2017 that left 13 people dead. The fire was started by a young boy playing with the stove in his family’s first-floor apartment.