A plane has crashed after a US airline employee conducted an "unauthorised take-off" in Washington state, officials have said.
Witnesses reported seeing the plane being chased by two F-15 military jets near Seattle-Tacoma International Airport before it crashed near Ketron Island.
The Pierce County Sheriff's Office said on Twitter that preliminary information suggested that a mechanic had stolen the aircraft.
The tweet said the crash may have been caused by the 29-year-old employee "doing stunts in air or lack of flying skills".
It added: "This is not a terrorist incident. Confirmed info.. this is a single suicide male. We know who he is. No others involved."
The sheriff's department said they were working to conduct a background investigation on the man, who they did not identify.
They added that the man could be heard on audio recordings telling air traffic controllers that he's "got a lot of people that care about me" and that he is "just a broken guy".
An airline employee conducted an unauthorized takeoff without passengers at Sea-Tac; aircraft has crashed in south Puget Sound. Normal operations at Sea-Tac Airport have resumed.
— Sea-Tac Airport (@SeaTacAirport) August 11, 2018
The US Coast Guard said it has sent a 45ft vessel to the crash scene after reports of a large plume of smoke in the air.
Alaska Airlines confirmed that a 76-seater Horizon Air Q400 aircraft had been involved in the "unauthorised take-off" and it believed no passengers were on board.
Horizon Air is part of Alaska Air Group and flies shorter routes throughout the US west.
Seattle-Tacoma International Airport officials said normal flight operations have resumed.
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