Flames shot out of the window of a third-floor unit just after 4:30 a.m. along West 135th Street.
Officials said that five people and one firefighter were taken to Harlem Hospital with non-life-threatening injuries.
Residents were forced to evacuate by using a fire escape.
The cause of the fire is under investigation.
The American Red Cross is assisting five households, for a total of eight adults and 11 children.
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