Flames engulfed an El Cajon business early Tuesday shutting down traffic to a portion of El Cajon Boulevard.
Heartland firefighters were called to the 700-block of El Cajon Boulevard just before 5 a.m.
The California Highway Patrol received a call from a driver traveling on nearby Interstate 8 reporting that the smoke was visible from the highway.
The fire began in a small building next to the Cottonwood Electric Car Service. Embers flew onto the larger building next door.
Despite getting water on the fire very quickly, it took crews more than an hour to gain control of the blaze.
Eastbound lanes of El Cajon Boulevard were closed until approximately 6:30 a.m. The westbound lanes were opened several hours later. The fire caused temporary delays for trolley service.
Investigators wrapped up on scene but have not released a cause of fire. One wall inside the building was unstable so they couldn't access all areas to find a direct cause.