Jet crashes after rogue employee steals Alaska Airlines plane in Seattle

He stole the plane [Photo: Courtesy]

A man stole and crashed a plane following an "unauthorised take off" at Sea-Tac Airport in Seattle on Friday evening, authorities say.

Video appears to show the plane, believed to be an Alaska Air Q400, flying overhead as a fighter jet follows in pursuit.

The Peirce Country sheriff’s office confirmed that it was not a "terrorist incident”.

Two F-15 fighter jets were scrambled to the location but were not involved in the crash, it added.

It is believed that the pilot was a 29-year-old mechanic who worked for another airline and had little knowledge of flying.

An audio recording reveals air traffic control communicating with the pilot as they attempt to guide him through aerospace.

Sea-Tac Airport confirmed on Twitter that the plane crashed in nearby on Ketron Island, near Puget Sound in Washington State.

Smoke at Ketron Island [Photo: Courtesy]

No other passengers were onboard the plane.

"An airline employee conducted an unauthorized takeoff without passengers at Sea-Tac; aircraft has crashed in south Puget Sound," the tweet read. "Normal operations at Sea-Tac Airport have resumed."

As the incident unfolded, one person wrote on Twitter: "SEATAC airport is on a ground halt because evidently a mechanic is flying an unauthorized flightseeing trip around the mtns.

"They wont let anyone leave the airport while he's up there. Pilot said it was most bizarre thing he'd heard in his career."

Another passenger who was waiting to take off tweeted: "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.

"The tower ordered a full stop and they’re trying to communicate with that pilot."

An Alaska Air statement read: "We are aware of an incident involving an unauthorized take-off of a Horizon Air Q400.

"We believe there are no passengers on board.

"We've confirmed a Horizon Air Q400 that had an unauthorized takeoff from SeaTac around 8pm has gone down near Ketron Island in Pierce County, WA."

Footage appears to show moments after hijacked Alaska Airlines plane crashed in Seattle