The fire broke out Friday at an apartment building on Washington Place in Passaic.
The three-story building was destroyed.
The fire chief says the flames apparently started in the first-floor apartment of a woman who was among the injured and is known to be a heavy smoker.
One resident, identified only as a 53-year-old woman, remained in critical but stable condition at St. Joseph's Regional Medical Center, while two other residents rescued by firefighters were treated there Friday for minor injuries and later released.
Two firefighters - one who dislocated his shoulder and another who may have broken one or more ribs - were also taken there for treatment.
Officials say the fire was reported around 4 p.m. Friday and burned for several hours. About 80 residents were displaced by the blaze.