Police and fire crews responded to the scene, in the 500 block of Grandview Avenue, at about 1 p.m. after receiving a report of a loud blast.
At the same time, four people who were in the home drove to Mason General Hospital in Shelton for treatment of injuries from the explosion. Two of them were later airlifted to Harborview Medical Center.
The victims are said to be three 20-year-olds and a 17-year-old.
Sources close to the investigation say the house was part of a marijuana grow operation and investigators suspect the explosion was caused by the process of extracting hash oil.
If confirmed, that would make it the second marijuana extraction blast in two days in the Puget Sound region. On Monday night a refrigerator exploded in a Lake City home as the unintended result of the resident extracting THC from marijuana.
Aerial footage from KOMO's Air 4 showed a blue house with a blown-out window on the side of the house towards rear.