Two toddler sisters died Wednesday after what authorities described as a "steam condition" caused by a malfunctioning radiator at the city-owned Bronx apartment building where they were staying while homeless, officials said.
The children, identified as Scylee Vayoh, 1, and Ibanez Ambrose, 2, were initially taken to a hospital in critical condition after fire officials say they got a call about a fire on Hunts Point Avenue around noon.
They died about an hour later.
Mayor de Blasio, who visited the building Wednesday, says the city is mourning the loss of the two children.
"We are in the preliminary stages of what is a highly active, multi-agency investigation into what happened in this home and whether there’s anything that can be done to help prevent such an unspeakable event in the future," he said. "Our law enforcement, buildings, fire and social services personnel will not rest until we can answer what has given rise to this heartbreaking incident."
The FDNY says a radiator valve malfunctioned inside the apartment and high-pressure steam shot out, filling the apartment. The two toddlers were severely burned and later died.
Neighbors told NBC 4 New York they heard a loud boom, and they left the building.
"The babies came out, they were burned all over the body -- burned blue, and there was no fire, so steam coming from somewhere," said Martiza Morales, recalling they "were not moving at all."
The children's parents ran out in tears, neighbors said.
"They were screaming for help. They say the radiator exploded in there," said Annie Martinez.
Radio transmissions between the dispatcher and emergency responders revealed a grim scene.
"It looks like it might have been something to do with a heater," the dispatcher could be heard saying. "We don't know if it blew up or what. But a heater injured those two kids, and they're in cardiac arrest right now."
"We got a lot of calls for smoke, so it looks like it might have been steam," the dispatcher added.
The city's social services department said after the blast that the children and their family were among five placed at the apartment building being used as a so-called "cluster site" for homeless family. The other families at the apartment are being moved to other shelters.
"We are devastated by this tragedy," the department said in a statement. "We are investigating and taking steps to immediately transfer the four other families being sheltered at this location to another shelter.”
City records show that the apartment where the blast went off had no open violations with the city, but that the building itself had 60 violations. There had been 46 complaints called into 311 this year for the building, including three for radiators.
One of the landlords of the building was on the city advocate's list of the 100 worst landlords. NBC 4 New York has reached out to the landlord's attorney for comment.
The investigation into the blast is ongoing.