PORTLAND, Ore. -- A door on an eastbound MAX train opened while the train was running Thursday morning and was ripped off its hinges after smashing into a metal box on a tunnel wall near Sunset Transit Center.

There were about 40 people on the train and nobody was injured. All the passengers were able to safely evacuate the train.

TriMet said the door, located on the left side of the train, had experienced a mechanical issue earlier Thursday. Because of the malfunction, the door was not in use at 11:30 a.m., when it opened and came off the train.

Service was restored by 1:15 p.m.

The box the door crashed into was an equipment box that contained lubrication for train operation.

Trimet spokeswoman Mary Fetsch said an investigation is underway to determine why the door was not effectively secured and how it was able to come off.