Updated at 10:52 a.m ET Saturday
A 29-year-old man stole a plane with no one else on board from Seattle-Tacoma International Airport late Friday before crashing on a nearby island, authorities said.
The man was a resident of Pierce County, Wash., and "acted alone," the Pierce County Sheriff's Department tweeted, describing him as "suicidal."
Alaska Airlines said it "believes" the man was a ground service agent working for Horizon Air. He took off without clearance at around 8 p.m. local time before crashing about an hour later, the company said in a statement.
The plane was in a "maintenance position," the company said, and was not scheduled for any passenger flights. Horizon is owned by Alaska Air Group, Inc., which also owns Alaska Airlines.
Reporter Austin Jenkins of Northwest News Network circled Ketron Island, the site of the crash landing, by boat Friday night. "There was smoke. We saw flames on the hillside, police boats circling, helicopters overhead," he told NPR's Scott Simon on Weekend Edition Saturday.
It appeared that nobody besides the pilot was harmed, Jenkins said. He told Scott the plane crashed into a forested area "where it didn't look like there were any homes in the immediate area." Ketron Island is small — about 230 acres -- and fewer than two dozen people live there, Jenkins said.
Pierce County Sheriff Paul Pastor told member station KNKX's Ed Ronco that the fire is "under control."
The sheriff's department said federal authorities would lead the investigation into the crash. The National Transportation Safety Board, Federal Aviation Authority and FBI have all been notified, Alaska Airlines said. President Trump was briefed on the incident, the White House said Saturday.
The sheriff's department initially described the man who stole the plane as a mechanic.
The man told authorities on the ground he "would like to apologize" to people who cared about him. "I'm a broken guy who had a few screws loose. Didn't really know it until now," the man said, according to audio from air traffic controllers.
Released radio conversation between the man and air traffic controllers goes on for more than a half hour. The man sounds calm at times and jokes with operators on the ground, who try to direct him to places to land.
Horizon Air Chief Operating Officer Constance von Muehlen said, "Our hearts are with the family of the individual aboard as well as all our Alaska Air and Horizon Air employees."
Two military F-15s chased the plane "within a few minutes of theft of plane" and "kept plane out of harms way and people on ground safe," the sheriff's department said. The F-15s were scrambled from Portland and were not involved in the crash.
People who said they were witnesses on the ground posted video on Twitter:
The Bombardier Q400 is a turboprop airplane made for shorter flights, according to Alaska Airlines. It has 76 coach seats and is about 108 feet long.
The airport says normal operations at Sea-Tac have resumed.