The mechanic was the only person on board

An airline employee's stolen a passenger plane and crashed in the US state of Washington.

It's understood the mechanic was the only person on board the 76-seater aircraft when it took off from Seattle.

Officials say it's likely the man died in the crash.

F-15s were scrambled from Portland and had "made it within a few minutes of theft of plane", Pierce County Sheriff's Office said.

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 was "just a broken guy".

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.

Footage was also posted on Twitter.

Horizon Air chief operating officer Constance von Muehlen confirmed one of its employees had made the "unauthorised take-off".

She confirmed no other crew or passengers had been on the 76-seater Q400.

Local sheriff Paul Pastor says there's no suggestion of terrorism.

"I understand the person may have been doing some air stunts and whatever.

"I know that some aircraft were scrambled from the Airforce Base - there was no indication that this person who was flying the plane was trying to damage anything or attack anything".