At least three people were killed on Saturday when a train went off the tracks in western United States, a local sheriff said.
Seven of the train's 10 cars derailed, a spokesperson of the railway company Amtrak said.
The National Transportation Safety Board said it sent a team of investigators and specialists to probe the incident.
The Empire Builder train running between Chicago and Seattle derailed in north-central Montana, a local official said.
Amtrak spokesman Jason Abrams said the train was carrying around 146 passengers and 16 crew members on board.
At least 50 people were injured, The New York Times reported, citing officials.
"Amtrak is working with local authorities to transport the injured passengers and move all other passengers to safety," the company said.
The incident took place at around 4 p.m. local time (2200 UTC), said Eric Weiss, a National Transportation Safety Board spokesperson.
Footage and images posted to social media showed several cars on their sides and passengers were standing alongside the tracks, some carrying luggage.
According to media reports, several passengers have been taken to a nearby high school.
Several Empire Builder trains were canceled after the incident, Amtrak said.