An airline mechanic stole an empty Alaska Airlines plane and took off from Sea-Tac International Airport in Washington state before crashing near a small island, officials said.

Preliminary information suggests that the 29-year-old mechanic stole the Horizon Air Q400 and the crash occurred because the person was “doing stunts in the air or (had a) lack of flying skills”, the Pierce County Sheriff’s Department said.

Witnesses reported seeing the plane being chased by military aircraft before it crashed near Ketron Island, south west of Tacoma, Washington. There were no passengers aboard.

Ed Troyer, a spokesman for the Pierce County Sheriff’s Department, said on Twitter that the man was unstable and that there was no connection to terrorism.

The sheriff’s department said they were working to conduct a background investigation on the man, whose name was not immediately released.

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

The US Coast Guard sent 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 US West. The Q400 is a turboprop aircraft with 76 seats.