WHITE SULPHUR SPRINGS, W.Va. | The train carrying Republican lawmakers to a multiday policy retreat crashed into a truck Wednesday, resulting in at least one fatality in the truck.

At least one member of Congress was examined at a hospital, and another member and a staffer who were on the train were examined for injuries.

One of the people in the garbage truck died, according to Jessica R. Towhey, a spokeswoman for the Congressional Institute, which is holding the three-day event at the Greenbrier resort in West Virginia.

“Our thoughts and prayers go out to this person’s family and to their friends,” Ms. Towhey said, adding that another person in the truck sustained “critical injuries.”

Rep. Jason Lewis, Minnesota Republican, was checked out at a local hospital as part of a standard concussion protocol.

“I’m fine compared to, tragically, the truck drivers, and thankful for the prompt action of our doctors and first responders,” Mr. Lewis said. “My thoughts are with the family of the individual who passed away.”

Ms. Towhey said others on the train were provided first aid.

A spokesperson for the group said the Republicans’ conference would proceed with an adjusted program. It will include a moment of prayer for those involved in the crash and a security briefing from the sergeant at arms and the U.S. Capitol Police.

Vice President Mike Pence was supposed to address lawmakers at a dinner Wednesday evening, and President Trump was to speak at the event Thursday.

Mr. Pence tweeted Wednesday that he still planned to head to West Virginia later in the day and that he and Mr. Trump will continue to monitor the situation. “Getting regular updates on the Amtrak crash involving members of Congress and their families. Praying for all involved & grateful for the swift action of first responders,” Mr. Pence tweeted.

The Amtrak train, a special charter for the event, crashed outside Charlottesville, Virginia. Amtrak said the incident occurred at 11:20 a.m. in Crozet, Virginia, and that two Amtrak crew members and two passengers were transported to a local hospital with minor injuries.

The University of Virginia Health System said five people had been transported to the UVA Medical Center or were en route, including one patient in critical condition.

The National Transportation Safety Board confirmed it has sent a team out to investigate the crash.

House Speaker Paul D. Ryan was on the train and was fine, according to his office.

It’s unclear how the collision occurred.

Several lawmakers reported that three people were injured, including one fatality, but the injured persons appeared to be on the truck, not the train.

“Three people, and I’m just looking out the window, a large, white, long dump truck. I think there were three people in that. I think one, we speculate, looks like one didn’t make it, there’s another one badly injured and we don’t know about the third,” Rep. Mark Walker, North Carolina Republican, told Fox News.

Speaking on a phone on the train, Mr. Walker said he was looking out his window at the scene. He described the crash as “a force” in which people were thrown.

“I was on the train near the front and obviously heard the impact, felt the impact, and it was loud, and it was harsh,” Sen. Jeff Flake, Arizona Republican, told CNN.

Rep. Tom Cole said some lawmakers who are physicians immediately tried to attend to the injured.

“They were administering CPR to folks who had been injured in the crash,” Mr. Cole, Oklahoma Republican, told CNN.

He said those who are trained physicians were the first on the scene prior to emergency medical services.

Mr. Flake said one person already had died when his colleagues tried to help. He said it appeared that the injured were ejected from the truck on impact or were riding on the back of the dump truck.

White House press secretary Sarah Huckabee Sanders said Mr. Trump had been briefed on the crash and was receiving regular updates.

“There is one confirmed fatality and one serious injury,” she said. “There are no serious injuries among members of Congress or their staff. Senior administration officials are in regular contact with Amtrak and state and local authorities. Our thoughts and prayers are with everyone that has been affected by this incident.”