FDNY officials say the fire broke out just before 3:40 p.m. at a six-story apartment building at 2609 Bainbridge Ave. and East 193rd and 194th streets in the Fordham section.
First responders were met with heavy fire shooting out of the a second-floor apartment up the interior stairs.
A search of the apartment turned up three children, who were removed from the building and taken to St. Barnabas in critical condition.
A 1-year-old boy, among the three children, was pronounced dead at the hospital. The two other children, believed to be 6-year-old twins, are in critical condition.
In total, five civilians were injured, including the three children, one adult civilian who was seriously injured and taken to a nearby hospital, and another who suffered minor injuries and refused medical attention.
In addition, three firefighters suffered minor injuries and were taken to nearby hospitals.
More than 20 units, and 79 fire and EMS personnel responded to the scene.
The fire was placed under control around 4:40 p.m.
FDNY officials believe that doors left open as occupants fled may have helped the fire spread, as has been the case in several recent fires in New York City.
The cause of the fire is under investigation.
Police say at least 10 people have been displaced.
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