The blaze erupted shortly after 3 p.m. Monday at the Paradise Mattress Co., at 781 Bushwick Ave., in the Bushwick section after witnesses reported a lightning bolt flash down in a thunderstorm and strike the rooftop.
Fire officials called it the city's biggest fire of the year.
Nine firefighters were injured; at least one was treated at a hospital. One civilian was treated at the scene.
More than 200 firefighters battled the fire for hours, bringing it under control by 8 p.m., Fire department spokesman Mike Loughran said.
The acrid smoke forced neighborhood residents to go indoors and close their windows. It was visible miles away in the Astoria and Long Island City sections of Queens.
Last December, one firefighter was killed while battling a four-alarm blaze in a mattress warehouse in Upper Manhattan.
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