"The train carrying GOP members to our retreat had a collision, but Rebecca and I are both okay," congressman Bradley Byrne said on Twitter, referring to his wife.
"Security and doctors on board are helping secure the scene and treat injuries."
Local authorities had yet to release statements about the accident, and the nature of the injuries was not known.
It was not clear in particular if any members of Congress were among those injured.
Paul Ryan's office said the Republican House speaker was "fine."
Vice President Mike Pence -- the keynote speaker at the three-day retreat west of the US capital -- was to fly in later in the day, and was not on the train.
House Republican Greg Walden tweeted a photograph of the scene, showing people standing off the train tracks next to a badly damaged truck, with debris strewn on the ground.
"We're fine, but our train hit a garbage truck. Members with medical training are assisting the drivers of the truck," Walden said.
"The train hit a garbage truck, they're asking for doctors on the trains to help," said the Twitter feed of congressman Roger Marshall, who is also a licensed physician.
"Right now Dr. Marshall is helping people who are injured."
Republican members of the House of Representatives and the Senate left Washington earlier Wednesday bound for the historic Greenbrier resort in White Sulphur Springs, West Virginia, for their annual retreat.
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