An airline mechanic stole an Alaska Airlines plane without any passengers and took off from Sea-Tac International Airport in Washington state on Friday night before crashing near Ketron Island, officials said.

　　In this file photo taken on September 25, 2006 Alaska Airlines planes are seen at Seattle-Tacoma International Airport. [File photo: AFP/Gabriel Bouys]

　　Preliminary information suggests that the mechanic stole the Horizon Air Q400 and the crash occurred because the person was "doing stunts in air or lack of flying skills," the Pierce County Sheriff's Department said on Twitter.

　　The plane was chased by military aircraft, witnesses said.

　　Sea-Tac officials said the airline employee had "conducted an unauthorized takeoff without passengers."

　　The U.S. Coast Guard was sending a 45-foot vessel to the crash scene after witnesses reported seeing a large plume of smoke in the air, Petty Officer Ali Flockerzi said.

　　Horizon Air is part of Alaska Air Group and flies shorter routes throughout the U.S. West. The Q400 is a turboprop aircraft with 76 seats.

　　A spokesman for the Transportation Security Administration directed inquiries to local authorities.