Air Alaska passengers wait in the terminal following an incident where an airline employee took off in an airplane, at Seattle-Tacoma International Airport in Seattle, Washington, U.S., August 10, 2018.
Sea-Tac Airport was put on an immediate ground stop once the plane took off.
Just after 10pm Pacific, Horizon parent company Alaska Airlines tweeted confirmation that "a Horizon Air Q400 that had an unauthorized takeoff from SeaTac around 8pm has gone down near Ketron Island in Pierce County, WA".
"Okay this insane. A pilot on the plane in front of us just went rogue and took off on an empty plane bypassing orders from the tower", tweeted Ben Schaechter, a passenger on an aircraft that was taxiing to take off before the incident.
Witnesses reported seeing the plane being chased by military aircraft before it crashed on Ketron Island, a small island in the Puget Sound that is home to about two dozen residents.
Seattle-based The Air Current.com Editor-in-Chief Jon Ostrower said that "being able to power on and do a rudimentary preflight and engine start on a commercial airliner is not only the purview of trained airline pilots".
After the plane approached Ketron Island, Waldron saw a thick column of smoke followed by a loud explosion, he said.
"The President has been briefed on the incident involving a stolen plane from Sea-Tac Airport in Seattle and is monitoring the situation as information becomes available", press secretary Sarah Huckabee Sanders said.
Two flights were delayed at Spokane International Airport because of the Sea-Tac delay.
Ed Troyer, a spokesman for the sheriff's department, said on Twitter the man was suicidal and there was no connection to terrorism.
He also said he was "just a broken guy, got a few screws loose I guess".
In one, the controller can be heard telling the pilot: "What we don't want to see is you get hurt or anyone else get hurt, so like I said, if you want to land, that's probably the best way to go".
The plane was a Q400, a Bombardier turboprop plane.
Air traffic controllers tried to talk the agent into landing but he refused. Well I would hope it would be for a guy like me'.
Horizon Air COO Constance von Muehlen said in a late-night video message "our hearts are with the family of the individual onboard as well as all our Alaska Air and Horizon Air employees".
The man told authorities on the ground he "would like to apologize" to people who cared about him. The F-15s were scrambled from Portland and were not involved in the crash.
"This is probably jail time for life, huh?" said Rich.
The sheriff's department initially described the man who stole the plane as a mechanic.
"My husband and I are recently former Boeing employees, and we were wondering why a jet was near the passenger airplane", she said.
Then the passenger plane pilot "did a complete loop. Never really knew it until now".