Starr Tyler, dispatcher at the Liberty Country Sherriff’s Office, told the Associated Press news agency that at least three people were killed in Saturday’s incident.
Amtrak said in a statement that there were multiple injuries.
“Amtrak is working with the local authorities to transport injured passengers, and safely evacuate all other passengers,” it added.
The cause of Saturday’s incident was not immediately clear.
US media said the train was headed for the city of Seattle from Chicago.
Photos posted to social media showed several cars on their sides. Passengers were standing alongside the tracks, some carrying luggage.
The images showed sunny skies, and it appeared the accident occurred along a straight section of tracks.
Megan Vandervest, a passenger on the train who was going to visit a friend in Seattle, told The New York Times that she was awakened by the derailment.
“My second thought was that’s crazy. We wouldn’t be derailing. Like, that doesn’t happen.”
She told the Times that the car behind hers was tilted over, the one behind that was entirely tipped over, and the three cars behind that “had completely fallen off the tracks and were detached from the train”.
Speaking from the Liberty County Senior Center, where passengers were being taken, Vandervest said it felt like “extreme turbulence on a plane”.
The National Transportation Safety Board said it will send a 14-member team, including investigators and specialists in railroad signals and other disciplines, to investigate the derailment.