"We called a third alarm because of the nature of the location and also because of the size of the building," Gert Zoutendijk from the Lake Oswego Fire Department told KATU News.
The flames charred several units at the Gables Apartments on Jefferson Parkway.
All of the residents were evacuated and no injuries were reported.
Six of the apartment units were damaged by flames and several more were damaged by water and smoke.
The total damage is estimated at $375,000.