Four residents were treated for smoke inhalation -- and a firefighter was hospitalized with heat exhaustion -- after a fire forced the evacuation of a Hempstead apartment complex Wednesday night, police said.

None of the injuries were life-threatening, but Nassau County police and fire officials said the blaze, which appeared to originate from a faulty extension cord, significantly damaged three apartments in the 64-unit complex at 621 Front St.

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The fire, which started in Apt. 3G, was reported in a 911 call at 8:34 p.m., police said. The entire complex was evacuated during the fire. About 80 firefighters staffing 15 trucks battled the blaze. Police said residents of all but the three damaged apartments were allowed to return after the fire.

An investigation determined the blaze was "nonsuspicious" and that it "originated from the electrical malfunction of an extension cord," police said.

Volunteers from Hempstead, West Hempstead, South Hempstead, Baldwin, Uniondale and Rockville Centre fought the fire. Ten ambulances also responded to the scene. The injured firefighter was from West Hempstead, police said, adding that all victims were treated and later released.