Fire crews arrived at the building in the 4900 block of Del Monte Avenue at about 12:30 a.m. Monday. They found smoke billowing from a corner of the building at street level.
Firefighters peeled off the stucco covering and found that a corner support pillar was burning. They quickly extinguished the fire, but as they inspected the building, they could not find anything that explained why the fire started.
"There was no electrical in that area. We're not exactly sure what could have caused it. There was nothing on the exterior that was a heat source," San Diego Fire-Rescue Department Battalion Chief Ty Shimotuchi said. "But right now, our main concern is not the fire but the structural integrity of the building."
Fire officials worried that the building was in danger of collapsing, so they ordered all of the residents to evacuate. They summoned a structural engineer. The engineer apparently determined that the building was safe, because everyone was allowed back inside after the inspection was complete.
Residents told FOX 5 they heard some loud popping sounds before discovering the smoke and they may have been caused by an explosion. But fire investigators said the sounds may actually have come from columns shifting on the unstable foundation.
The cause of the fire remained under investigation.