A rear bedroom at Gateway Condos on Sparta Avenue went up in flames shortly after 4 a.m., the Newton Fire Department said.
Nobody was found inside the apartment during a search by fire crews, who worked quickly to put a line into service and get control of the blaze, officials said.
The scene was cleared within about two hours, and no injuries were reported in the fire, the department said.
Fire crews in Andover, Sparta, Fredon and Hampton also assisted at the scene.
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