A fire in the photo lab and classroom at Clovis West High School caused heavy damage to the building, the Fresno Fire Department reported Wednesday night.
A general fire alarm sounded about 7:25 p.m. Custodians reported it as a false alarm.
But an arriving fire engine spotted smoke coming from the roof of the Crafts Building on the north side of the campus and requested additional fire engines.
Fire crews encountered heavy smoke in the 7,000 square foot building, but were able to extinguish the fire. Heavy fire damage was confined to one area of the building, but smoke damage occurred throughout the rest of the building.
One custodian was treated at the school for smoke inhalation.
Fire Capt. Domlin Juul said the cause appeared to be electrical. He did not have a dollar figure for the loss.
Clovis Unified School District spokeswoman Kelly Avants said some classes will be relocated Thursday, but school will open as usual.
Check fresnobee.com for breaking news.