At least 19 people, including nine children, have died after a fire in a New York apartment building.
Another 32 people were sent to hospital, several of whom are in a critical condition, according to New York Mayor Eric Adams.
Fire department Commissioner Daniel Nigro said they had found victims on every floor of the 19-storey block, saying the smoke was "unprecedented".
He told NBC News the death toll was the worst seen in New York for 30 years.
It comes days after an apartment fire in Philadelphia killed 12, with eight children among the dead.
Sunday's fire broke out in an apartment that spans the second and third floors of the Bronx apartment block at about 11:00 local time (16:00 GMT), officials said.
Some 200 firefighters were sent to tackle the blaze, which officials believe was sparked by a malfunctioning electric heater.
Commissioner Nigro said there were two floors of fire, but the smoke had spread everywhere.
The door to the apartment where the fire started was left open, and smoke then spread to every floor, Commissioner Nigro told reporters.
"Members found victims on every floor in stairwells and were taking them out in cardiac and respiratory arrest," he said.
In a virtual news conference on Monday, Andrew Ansbro, the president of the firefighters' union, said the building was "well-known in that area, for having difficult fires", noting that its fire protection rules with regard to sprinklers and self-closing doors may have been different from those of the city.
He claimed it was because the building had previously received federal subsidies and therefore was not required to follow the same fire codes.
Mr Ansbro also said that Covid-19 had affected the staffing levels of first responders.
George King, who lives nearby, told AFP news agency people were waving from the windows as the flames took hold.
"I saw the smoke, a lot of people were panicking," he said. "You could see that no-one wanted to jump from the building."
A total of 63 people suffered injuries, including the 32 taken to hospital. Thirteen are in a critical condition, Stefan Ringel, a senior adviser to the mayor, told AP news agency., external
"The impact of this fire is going to bring a level of pain and despair to our city," Mr Adams told reporters. "The numbers are horrific."
He told CNN on Monday that the incident was "a wake-up call for all our buildings" to ensure complaints are heard and protective measures are working.
New York Governor Kathy Hochul called Sunday's events "a night of tragedy", and pledged to create a victims' compensation fund to support survivors.
"There will be money to find new housing, burial costs and whatever we need because that's what we do here in New York," Ms Hochul said.
The area of the Bronx where the fire occurred is home to a large Muslim immigrant population and many of those affected by the blaze are believed to have originally come to the US from the Gambia.
Mr Adams urged anyone impacted by the fire to seek assistance from the authorities, irrespective of immigration status. He assured residents that their details would not be passed on to immigration services.
Speaking alongside Mr Adams, New York Senator Chuck Schumer pledged to provide immigration support to allow families to come together to grieve.
The building hosts a number of affordable housing apartments and the blaze is likely to raise questions over the quality of such units in the city.
Representative Ritchie Torres, a Democratic lawmaker whose district includes the building, told the US network MSNBC that developments such as the building where the fire hit 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," Mr Torres said.
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