Video from the scene shows the plane, which had no passengers on board, fly upside down while being tracked by fighter jets. It crashed on the south of Ketron Island, near a military facility.
Alaska Airlines planes are seen at Seattle-Tacoma International Airport in SeaTac, Wash., Oct. 30, 2013.
Local sheriffs, while speaking to news agency AFP, have confirmed that the plane crash was "not a terrorist incident".
Police described him as a "suicidal male" and confirmed he is local.
"Our hearts are with the family of the individual aboard as well as all our Alaska Air and Horizon Air employees, "she said in a video message".
The plane, which PCSD identified as belonging to Horizon Air, crashed into Ketron Island.
Authorities said an airline employee had made "an unauthorised take-off" without any passengers on board.
Some Seattle-bound flights were diverted to Vancouver.
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The stolen plane was a twin engine turboprop Q400 airplane belonging to its sister carrier Horizon Air, Alaska Airlines said on Twitter. He is flying around the airport, he does not know how to land it. Happening right now.
"Congratulations, you did that, now let's try to land that airplane safely and not hurt anybody on the ground", an air traffic controller said. "I don't know what the burnage is like on takeoff, but it burned quite a bit faster than I expected". "Normal operations at Sea-Tac Airport have resumed". "Holy smokes, I've got to stop looking at the fuel because it's going down quick".
Freaky audio from the cockpit reveals how air traffic control tried to talk him into landing the plane.
Only the unidentified pilot was on the plane, according to authorities. "Military jets were scrambled from Portland, but it does not appear that these jets were involved in the crash of the Horizon aircraft".
"I would like to apologize to each and every one of them", the man added. "We frequently get involved with matters related to aircraft so we are poised to act if information develops to suggest a federal criminal nexus".
The man could be heard on audio recordings telling air traffic controllers that he is "just a broken guy".
The Q400 is a 76-seater turboprop aircraft. "I was kind of hoping that was going to be it, you know".
Two F-15s were scrambled from OR to give chase to the plane.