An airline employee who stole an empty passenger plane from Seattle airport has crashed on a nearby island.

Authorities said the man had made "an unauthorised take-off" late on Friday local time, forcing Seattle-Tacoma International Airport to close.

Two F15 fighter jets pursued the plane. It is unclear if the man survived the crash in Puget Sound.

The Pierce County Sheriff's Office said it was "not a terrorist incident", adding the man was local and aged 29.

Pierce County Sheriff Paul Pastor later told reporters it appeared to be "a joyride gone terribly wrong", according to ABC7 News, adding "most terrorists don't do loops over the water".

Air traffic controllers tried to encourage the man to land before the plane crashed, a recording being shared online reveals.

The Seattle Times describes the man as sounding "carefree and wild", while a number of videos on social media show the plane flying over the area in an erratic manner.

The plane was a Horizon Air Q400, according to a statement from Horizon's partner airline Alaska Airlines. It crashed on the south of Ketron Island, near a military facility.

In the audio recording, the man can be heard starting to worry about how much fuel he had on board. He also suggests he could land the aircraft by himself because he had played "some video games".

The man, who is referred to by what is believed to be his first name, also discusses:

- The co-ordinates for the orca carrying her dead calf on her back

 - Looking at the view and possibly going to look at the Olympic Mountains, in Washington State

 - If he can do a barrel roll before landing and "calling it a day"

 - Whether or not Alaska Airlines would give him a job after a successful landing

Passengers queue at Seattle airport after the plane was stolen

Leah Morse, who filmed the jet flying overhead, told news agency Reuters she felt in her "gut something was wrong" after spotting the plane.

Ms Morse's mother, who lives close to the area where the plane went down, said her whole house shook.

"We saw the jets circle back after and she texted that there was no plane," she added.

Sheriff Pastor told KIRO7 news station in Seattle the man had most likely been killed in the crash.

Ben Schaechter was on a plane which was apparently taxiing down the runway as the stolen plane took off.

"Okay this insane," he tweeted. "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. Whaaaaaat!"

Passengers collecting their luggage at the airport appeared to be unclear about what exactly had taken place.

"They said there was some kind of emergency somewhere on the runway, and after that we just sat there for 40 minutes," one told Reuters. "But of course everyone's pulling out their phone and finding out what's going on and seeing this crazy story.

"Now we don't really know what happened, but hopefully everyone's OK."

The Q400 is a twin-propeller aeroplane with up to 78 seats, depending on configuration.

In a statement, the airport said: "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."

The airport said flights to and from Seattle-Tacoma had resumed. It is unclear how the employee managed to take the plane.