All flights were grounded at Seattle-Tacoma international airport in the US when a passenger plane took off without permission.
In this file photo taken on September 25, 2006 Alaska Airlines planes are seen at Seattle-Tacoma International Airport. Photo: AFP or licensors
Authorities said an airline employee had made "an unauthorised take-off" without any passengers on board.
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 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".
According to the Seattle Times, air traffic control, who referred to the man by what is believed to be his first name, tried to encourage him to land.
The newspaper describes him as sounding "carefree and wild" in the audio.
A number of videos on social media show the plane flying over the area in an erratic manner.
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 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. Separate audio, being shared on social media, seems to suggest the man thought he could land the aircraft by himself because he had played "some video games".
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 closer 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.
A message from Horizon Air Chief Operating Officer Constance von Muehlen: https://t.co/BDhk9pf1Yt
— Alaska Airlines (@AlaskaAir) August 11, 2018
Sheriff Pastor told KIRO7 news station in Seattle the man had most likely been killed in the crash.
The Q400 is a twin-prop 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."
- BBC
