Fire crews responded to the blaze in the 5400 block of West Santa Monica Boulevard at about 7:10 a.m. The fire was burning on the second floor and the attic of the building.
After about 25 minutes of fighting flames, crews were ordered to assume a defensive posture and fight the fire from the exterior, as the fire began to burn through the roof of the building.
It took 148 firefighters to knock the fire down in an hour and 39 minutes, an LAFD spokesperson said.
No injuries were reported from the incident. Eastbound and westbound traffic was shut down on Santa Monica Boulevard during the fire fight.
The cause of the fire has not been determined. Deputy Chief Joseph Castro said the building was built before 1933. Investigators say the fire may have been electrical and may have been smoldering for hours overnight.
City News Service contributed to this report.