Officials said winds drove flames to the north side, then back south. More than 170 firefighters were on the scene.
One firefighter had minor injuries and a child from an adjacent building was being evaluated for breathing problems. A third minor injury was also reported but officials did not immediately give details.
The four-story, 40-unit mixed-use building houses the Plaza Business Institute school and several businesses, including office and medical space. It is near the Roosevelt Avenue subway stop and the Brooklyn Queens Expressway.