The "heavily involved" blaze was reported shortly before noon in the 3500 block of S. Centinela Avenue, according to Los Angeles City Fire Department officials.
The fire happened within a common attic shared by a row of seven one-story businesses, fire officials said.
No injuries were reported as more than 100 firefighters fought the blaze in the 69-year-old building.
LAFD officials declared the "major emergency" fire a knockdown shortly before 1:30 p.m. Nearby streets were closed during the mop up.
The cause of the blaze was not yet known.
Meantime, about 945 Los Angeles County Department of Water and Power customers were without power in Mar Vista. An LADWP spokesperson said they could not immediately confirm whether the outage was a result of the fire.