Finnish authorities are investigating a bizarre incident in which a pilot was killed by a plane door which became detached from the plane. He was preparing a private jet for a flight when it happened.

The Gulfstream G150 jet, usually used for private flights arrived at the Kittila airport in northern Finland from Moscow, the Ilta Sanomat reports. It was being prepared for its next flight from the popular holiday resort in the Lapland region to Yekaterinburg, Russia on Thursday. 

"The plane flew from Moscow with the Russians on board, they were supposed to fly to Yekaterinburg," the newspaper said.

The plane which can seat 20 passengers was empty when the captain, the second pilot and a flight attendant boarded the aircraft for pre-flight checks. At that moment, the door detached from the fuselage and hit the pilot. It came off with such force that the 50-year-old man died on the spot, while parts of the door were then found some ten meters away from the aircraft, investigators say.

Describing the fatal accident as "very exceptional," Finnish authorities say they now consider a technical failure as its main cause. They have contacted officials in Austria where the plane is registered, as well as the US manufacturers of the aircraft.