The East Pierce Fire union said just before 10 a.m. that a janitor at Endeavour Intermediate School in Milton reported smoke and flames in the ceiling of the building.
Crews responded to 1304 17th Avenue and found a smoke-filled custodial room, East Pierce Firefighters IAFF Local 3520 said.
School was not in session, and the one person in the building was accounted for, according to the union.
They said the situation had been resolved about 10:30 a.m., and identified the source as an electrical issue.
Damage, which was contained to the one area, was minor, the union said.
No one was injured, East Pierce Battalion Chief Rick Getz said.
An overheated motor in the janitor closet caused the smoke, Getz said.