Numerous residents were rescued after firefighters arrived on University Avenue just after 11:15 p.m.
Three residents were pulled from an apartment on the rear of the second floor, where the fire is believed to have started.
Those residents, a 50-year-old man, a 34-year-old woman and a 4-year-old child, were in critical condition.
Firefighters from Ladder 46 also rescued two residents, a man and woman, from a fifth-floor window.
The man severely cut himself while trying to break through the window to escape. He and the woman were also treated for smoke inhalation.
Three firefighters were also treated, mainly for shoulder and back injuries.
The victims were taken to North Central Bronx Hospital and New York Presbyterian Hospital.
The fire spread heavy smoke throughout the building, prompting numerous residents to be overcome by thick smoke. Firefighters believe the configuration of the building contributed to the smoke spreading through the stairwell and hallways.
The fire took about an hour to get under control. The cause was not immediately known.
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