Hospitals worked Monday to save the lives of multiple people gravely injured by smoke in a fire that killed 19 people, including nine children, in a Bronx apartment building.

Dozens of people were hospitalised, and as many as 13 were in critical condition after Sunday’s blaze, already New York City’s deadliest in three decades. Investigators determined that a malfunctioning electric space heater, plugged in to give extra heat on a cold morning, started the fire in the 19-storey building.