At least 19 people, including nine children, lost their lives in a fire in a Bronx apartment buildling in New York City on Sunday, Mayor Eric Adams confirmed.

"We've lost 19 of our neighbors today. It's a tragedy beyond measure. Join me in praying for those we lost, especially the 9 innocent young lives that were cut short," Adams tweeted.

Earlier, the mayor told reporters: "This is a horrific, horrific, painful moment for the city of New York, and the impact of this fire is going to really bring a level of just pain and despair in our city."

"This is going to be one of the worst fires we have witnessed during modern times."

Thirty-two people were sent to hospital in life-threatening conditions. Nine people were also seriously injured, and 22 others sustained non-life-threatening injuries. One member of service was also removed to the hospital, said Adams.

The fire started from a space heater in an apartment that spanned the second and third floors of the building and only made it to the hall, city officials said.

But smoke still spread to every floor of the building, likely because the door to the apartment was left open, the city's fire department commissioner Daniel Nigro told reporters at a news briefing.

"Members found victims on every floor in stairwells and were taking them out in cardiac and respiratory arrest," Nigro said.

Fire marshals determined through physical evidence and accounts from residents that the fire started from a portable electric heater in the apartment's bedroom, Nigro said.

He added the heat had been on in the apartment building, and the portable heater had been supplementing that heating.

The catastrophe was likely to stir questions on safety standards in low-income city housing. This was the second major deadly fire in a residential complex in the U.S. this week after 12 people, including eight children, were killed early on Wednesday when flames swept through a public housing apartment building in Philadelphia. 

U.S. Representative Ritchie Torres, a Democrat whose district includes the New York building, told MSNBC that affordable housing developments such as the Bronx one pose safety risks to residents. 

"When we allow our affordable housing developments to be plagued by decades of disinvestment, we are putting lives at risk," he said.

Adams said many of the residents were from the small West African country of Gambia. The Gambian consulate in New York did not immediately respond to a request for information.

(With input from agencies)