An Amtrak train derailed Monday near Tacoma, Wash., and photos from the scene showed at least one rail car hanging off a bridge over traffic-clogged I-5.

"We are aware of an incident involving Amtrak train 501," Amtrak said in a statement. "We will update with additional details as they become available."

Amtrak Cascades trains connect 18 cities along the I-5 corridor including Seattle, Portland, Vancouver, British Columbia, and Eugene, Oregon. 

"Skip traffic," Amtrak says on its promotional material for the Cascades trains. "Take the train."

The National Transportation Safety Board said it was "gathering information" about the accident.