(Dallas, OR) -- An investigation is ongoing into a house fire that killed three people and seriously injured a fourth in Dallas. Firefighters responded to the 900-block of East Ellensdale Avenue early yesterday on reports of a fire. The Polk County Sheriff's Office says three people were found dead inside the burning home. Another three people were able to escape the blaze. One of them was rushed to a hospital with significant injuries, while the other two were treated for minor injuries at the scene. It's not yet clear what sparked the blaze.