At least three people have been killed and 50 others hurt after a train came off the tracks in the state of Montana.
Several carriages from the Amtrak Empire Builder passenger service derailed at about 16:00 local time (22:00 GMT) near the town of Joplin.
Images on social media show train cars on their sides and luggage strewn on the ground with people standing nearby.
Amtrak said there were some 141 passengers and 16 crew aboard the Chicago to Seattle service.
Passenger Megan Vandervest, who was heading to see a friend in Seattle, told the New York Times she was woken up by the derailment, which felt like "extreme turbulence on a plane."
Wayne Freed said that he was in the lounge car, one of those that flipped on its side, but was able to grab hold of a coffee table bolted to the floor.
"I just held onto that, and my legs were dangling down below and the windows broke out down below and which is how we eventually escaped after the train stopped," he told CBS.
"But I'd hate to think what would happen if I hadn't been able to hold onto my table."
Rescuers have been working to evacuate passengers, Amtrak said.
In a tweet, state Senator Steve Daines said he was "closely monitoring this situation".
"I am thankful for the first responders already on the scene and praying for the safety of all involved," he added.
The US National Transportation Safety Board has launched an investigation into the incident.
Though derailments of Amtrak trains are rare, there have been several in recent years.
In 2018, three people were killed when an Amtrak train travelled on to the wrong track and hit a parked freight train.