Firefighters were still on scene as of Sunday afternoon looking into the cause.
About 150 firefighters responded to the blaze at the two-story building near Olympic Avenue and Maple Street. It took crews about an hour and 40 minutes to put out the blaze.
One firefighter suffered a cut on his arm. He was taken to Los Angeles County-USC Medical Center, where he was treated and released. No other injuries were reported.
The block along Maple Avenue just south of Olympic Boulevard is filled with independent retailers and wholesalers. The fire caused damage to four businesses.
City News Service contributed to this report.