SEATAC, Wash. >> A jet bridge dropped several feet Tuesday as passengers were exiting a Southwest Airlines flight at Seattle-Tacoma International Airport, but no one was injured, officials said.

The end of the walkway, where it was attached to the plane, fell 6 to 8 feet. Some passengers were on the bridge at the time, but it was unclear how many, said airport spokesman Perry Cooper.

The cause of the drop was described as a mechanical failure. Thanks to a backup system — a large screw under the jetway that turns as it is raised or lowered — the bridge fell slowly, and those who were on it walked up to the gate, Cooper said.

About half of the passengers — 60 people — had exited the aircraft when the walkway fell. The rest left by a stairway brought to the other side of the plane.

A canvas covering designed to protect passengers from the weather also caught on the aircraft’s door, pulling the nose of the plane toward the ground. The plane was taken out of service pending inspections for possible damage, a Southwest Airlines official said.

By Tuesday afternoon, crews had brought in a large crane to lift the walkway and allow the plane to back away from it.

The plane, operating as Flight 570, had arrived from Phoenix and was supposed to continue on to Chicago’s Midway International Airport.

Michelle Agnew, a spokeswoman for Dallas-based Southwest Airlines, said in an email that the company is thankful no one was hurt.

The airline was working to accommodate passengers whose travel plans were affected, she said.