A plane has been stolen from Seattle-Tacoma international airport by an airline employee and crashed, authorities have confirmed, after F-15 fighter jets were scrambled and flights grounded in a major security incident.

Military pilots contacted the rogue aircraft and it crashed soon afterwards, said local media, citing sources at the US air force Joint Base Lewis–McChord (JBLM) in Washington state. The plane came down on Ketron Island in the Puget Sound waterway about 25 miles south-west of the airport on Friday evening. Aerial television footage showed a fire in amongst trees.

A law enforcement spokesperson said the incident was a suicide. The pilot was described as a 29-year-old ground service agent. The man had crashed by “doing stunts in air or lack of flying skills”, the Pierce County sheriff’s department said on Twitter. It is unclear whether the man survived the crash.

An Alaska Airlines spokesperson said the plane had been positioned in a maintenance area of the airport when it was taken. It had not been scheduled for passenger flight.

On Saturday morning, White House press secretary Sarah Sanders said in a statement that President Donald Trump was monitoring the situation.

The emergency shut down the airport, known as Sea-Tac, and the surrounding skies. The plane involved was a Horizon Air Q400 with no passengers on board, tweeted Alaska Airlines. Videos posted online showed an aircraft matching the description being followed by what appeared to be a fighter jet.

Strategic Sentinel (@StratSentinel) Video of the stolen Q400 out of @SeaTacAirport being chased by an F-15 pic.twitter.com/L2RhTJnpga

Recordings of an air traffic control conversation with the 29-year-old pilot supported the suicide claim. “This is not a terrorist incident,” said the Pierce county sheriff’s office, calling it a “suicide, single male”.

Paul Pastor, the county sheriff, said there was no indication the person flying the plane had intended any harm to others. “Our information now is there was only one person on the plane. I understand the person may have been doing some air stunts or whatever. Some aircraft were scrambled from the air force base. There was no indication this person flying the plane was trying to damage anything.”

Pastor said the man “did something foolish and may well have paid with his life”.

The man could be heard on audio recordings telling air traffic controllers that he is “just a broken guy.”

Flights were grounded with some passengers tweeting that their plane stopped abruptly on the runway. The Q400 is a twin-engined propeller plane made by Bombardier and sometimes referred to as a Dash-8. Horizon Air is a division of Alaskan that flies short routes in the western US.

Royal King told The Seattle Times he was photographing a wedding when he saw the low-flying turboprop being chased by two F-15s. He said he didn’t see the crash but saw smoke.

“It was unfathomable, it was something out of a movie,” he told the newspaper. “The smoke lingered. You could still hear the F-15s, which were flying low.”

Facebook Twitter Pinterest A Bombardier Q400 of the type involved in the Seattle incident. Photograph: George Rose/Getty Images

Air traffic controllers and pilots could be heard discussing the “ground stop” and dealing with a backlog of aircraft in the aftermath of the drama.

The Horizon Air chief operating officer, Constance von Muehlen, confirmed the plane was taken by a Horizon Air employee. “Our hearts are with the family of the individual aboard, as well as all our Alaska Air and Horizon Air employees,” von Muehlen said by video.

Airline employees told KIRO/7 News the plane had been parked at a cargo terminal when it was taken. According to the Seattle CBS affiliate, the pilot then entered the line of outbound planes and took off around 8pm local time.

Ben Schaechter (@Bensign) Halfway down the runway on Alaska airlines out of Seattle and the pilot slams on the brakes and shares we must go back to the gate. Quite a scary experience. Not entirely sure what’s happening. Someone sneak on board?

Air National Guard F-15 fighter jets based in Portland, Oregon, rushed to the area within minutes of takeoff. Arriving ahead of sonic booms, they tailed the airliner for 45 minutes as it circled over suburban areas south of Seattle. The chase passed over a the Chambers Bay golf course, which hosted the US Open in 2015, before the pilot began turning barrel rolls over the Puget Sound.

“It was low enough we could make out the Alaska face … so it was really low,” witness Ken Schmidtke told KIRO.

The plane crashed in a wooded area of Ketron Island, a speck in Puget Sound believed to be home to 12 people. Firefighters and police boarded a ferry to extinguish the blaze and begin an investigation.

The Washington state governor, Jay Inslee, praised the fighter pilots: “Those pilots are trained for moments like tonight and showed they are ready and capable,” the governor said on Twitter.

While a criminal investigation is expected, the National Transportation Safety Board will conduct the most detailed review of the incident. Security concerns raised by the crash will be addressed as well.

Flights through Sea-Tac airport had hours-long delays running well into the night. Flights diverted to other airports in the region arrived later that evening. Summer weekends are particularly busy at the Seattle area’s only major airport as Alaska-bound tourists pour into the region.