Nineteen people have died in what Bronx fire services are calling the worst fire the city has seen in decades.

NBC reports that at least 63 individuals have been injured, of whom 32 are considered to be in critical condition, with nine more in serious condition. Firefighters who rushed into the building reported seeing people on every floor suffering from severe smoke inhalation and cardiac arrest.

The dead number 10 adults and nine children.

Fire investigators have identified the source of the blaze as a duplex apartment on the second and third floors of the Twin Parks building on the Bronx's East 181st Avenue, in the Fordham Heights area.

The fire commissioner noted that the blaze included an unusually high quantity of smoke.

Fire services estimate that it took approximately 200 members of the department to fully contain the fire, working from 11:00 am to 1:00 pm.

Police reported that nearby Angelo Patri Middle School on Webster Avenue has been opened for any of the residents displaced by the blaze.

FDNY Commissioner Dan Nigro said residents were rescued on multiple floors by firefighters, after being trapped by the smoke and flames.

"There were certainly people trapped in their apartments all through this building," Nigro said. A number of residents found were suffering from cardiac or respiratory arrest, Nigro added.

New York City Mayor Eric Adams called the blaze one of the worst in the city's history.

"This is a horrific, horrific, painful moment for the City of New York," he said.

"This is going to be one of the worst fires we have witnessed here in modern times in the City of New York."

"When there is a crisis in this city or state, we are in this together … And we won’t succeed if we’re not united," Adams said during a news conference.

He added that "it appears as though this stemmed from a space heater."

Adams confirmed the building had a large Muslim population – with many residents from Gambia – in the building.

The death toll in Sunday's fire has already surpassed disastrous blazes in 2017 and 2007, making it the deadliest fire in the city since the Happy Land club was torched in an arson in 1990, killing 87 people.