A 5-year-old boy suffered burns to his leg, while a 4-month-old suffered smoke inhalation.
The blaze erupted on the first floor of 941 Intervale Avenue in the Morrisania section at 5:30 p.m. Sunday. It blocked residents' path, forcing everyone to use the fire escape.
Firefighters believe that someone set a mattress on fire in the lobby of the six-floor building.
Nearly two dozen people had to be rescued after heavy smoke forced them out on to the fire escapes.
Officials say two people are in critical condition and two are listed in critical but stable condition. One of the injured was a woman who fell from the fire escape.
Three firefighters suffered minor injuries.
The cause of the fire is under investigation.
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