South King Fire and Rescue firefighters responded to a fire this morning at a vacant commercial building.

Located at 31515 20th Ave. S., a passerby called 911 to report the burning structure at approximately 6:30 a.m.

Firefighters found smoke and flames from the roof on the back side of the building, according to Capt. Jeff Bellinghausen. Over the years, several tenants have used the building, including most recently the Federal Way school district office. The building currently does not have a tenant nor is it being remodeled.

Three engines, one ladder truck, one aid car and a battalion chief initially responded. But because of the size of the building, the difficulties in accessing a securely boarded up building and the nature of the fire, a second alarm was called for bringing an additional four engines and a ladder.

There was little fire damage inside the building but a large amount of smoke damage. The extent of damage to the roof and overhang is still being determined. Investigators are on scene and expect to have a cause determination later today.