LA MESA–An unoccupied commercial building in La Mesa was heavily damaged in a structure fire, Heartland Fire and Rescue spokesman said Friday.

At 5:52 p.m., firefighters from La Mesa with assistance from Cal Fire, San Diego Fire, and Santee Fire were dispatched to reports of a structure fire in the 4300 block of Palm Avenue. Fire crews discover heavy fire and smoke coming from the rear of a single-story building.

The building had a construction fence around it. Fire crews gained entry through the fence and began to attack the fire from the interior. Within 10 minutes, fire crews exited the building due to a partial building collapse and began to fight the fire in a defensive mode, attacking the fire from the outside. The fire was under control within 30 minutes. There were no occupants in the building and no firefighter injuries.

The cause of the fire is still under investigation.