The plane has crashed, according to Pierce County Sheriff's Department.
Alaska Air reports that a Horizon Air Q400, which is a twin propeller airplane, was stolen.
The unauthorized pilot was described by the Pierce County Sheriff's Department as a "suicidal male".
An airline mechanic who stole a Horizon Air plane from a Seattle airport told air traffic controllers that he was a "broken guy" but also joked about whether the airline would hire him as a pilot if he landed safely.
"We are aware of an incident involving an unauthorized take-off of a Horizon Air Q400", according to a statement by Horizon's parent company Alaska Airlines, posted at 9:16 p.m. Seattle time. It noted that normal operations at the airport had resumed. The tweet said the crash may have been caused by the mechanic 'doing stunts in air or lack of flying skills'.
According to the mercurynews.com, witnesses reported seeing the Bombardier Q400, a turboprop aircraft, perform a loop-the-loop and almost slam into Chambers Bay, all while being pursued by fighter jets.
Leah Morse, who filmed the jet flying overhead, told news agency Reuters she felt in her "gut something was wrong" after spotting the plane.
Two F-15 fighters were scrambled from the Portland airport and followed the plane as it flew over the region, the Federal Aviation Administration reported. It crashed on the south of Ketron Island, near a military facility.
His motive is not clear, but audio between the cockpit and air traffic control indicates the man was in emotional distress. The identity and condition of the pilot are not known.
He said the plane crashed in a wooded area.
"I felt like we were on the ground and we were safe, we weren't in the sky while something was going on", he said after getting off the plane.
"It was unfathomable, it was something out of a movie", King said.
Fighter pilots from the Air National Guard of Washington and OR flew alongside the plane, according to an emailed statement from Gov. Jay Inslee.