Cal Fire said at least 25 structures had burned.
The flames at the two-story structure were extinguished in about 10 minutes.
The fire was above a commercial laundry equipment store in the Borough Park neighborhood of Brooklyn.
An online video shows rapid fire spread during a DJ's pyrotechnics show and people's attempts to escape the raging flames.
She was in town checking out the 100-plus-year-old building for a potential project.
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