Firefighters were called to a strip mall that erupted in flames early Wednesday in Norwalk.
The blaze was reported shortly before 2 a.m. in the 11000 block of East Rosecrans Avenue.
Video showed heavy fire still burning through the roof of the structure at 4 a.m. as crews poured water on the flames from ladder trucks.
Five businesses appeared to be involved in the fire, which had gutted the building.
There were no reports that anyone had been injured in the incident.
The cause of the fire was under investigation.