Firefighters Wednesday night extinguished a blaze in an abandoned building at 650 Hamilton St. in Costa Mesa.
Officials are investigating whether squatters at the building, which used to house Port Mesa Christian School, caused the incident.
About 24 fire personnel responded to the structure at about 7:55 p.m. Wednesday, acting Battalion Chief Chris Coates said.
The structure was empty when firefighters arrived to find smoke coming from attic vents and multiple windows.
After forcing entry, they quickly extinguished flames burning in an area of about 20 feet square on the floor, Coates said.
Any damage was mostly caused by smoke, Coates said, and there were no injuries reported.
Investigators found evidence of squatters at the building and are working to determine what sparked the blaze.
"Because there were squatters inside and it's an abandoned building, we're going to investigate it and see if it was arson, just to determine the cause," Coates said.
— Jeremiah Dobruck