White House spokeswoman Sarah Huckabee Sanders said President Donald Trump was briefed on the accident.
A GOP aide said the train had partially detailed. Buses are en route to pick up the legislators to take them on to the retreat.
From his vantage point, he couldn't see the crash scene.
Officials say three people were in the dump truck, which was stalled on the tracks.
Update: It has been learned that Congressman Scott Taylor (R-VA) also was not on the train.
Both House and Senate members were on board the train, though it's unclear how many.
"Our thoughts and prayers are with everyone that has been affected by this incident", the White House said. Thom Tillis, R-North Carolina Sen.
Rep. Tom Cole, R-Okla., said the collision happened without warning, while many members were up and milling around the train.
There are now fears that one person was killed when the collision occurred in West Virginia.
The retreat will still take place this weekend, according to the Congressional Institute.
"I am in train that collided with a trash truck".
The crossing has a guard bar and signal lights.
Comer says lawmakers, spouses, and aides had been on the train for about two hours when suddenly there was a crash. Pence said he was praying for all involved & grateful for the swift action of first responders.
The train carrying the lawmakers hit a garbage truck south of Charlottesville, Virginia. The Tennessee congressman was thrown around and suffered neck, back and foot injuries. Five patients were transported to UVA Medical Center, with one in critical condition, the hospital tweeted. "I'm in a whole lot of pain and discomfort".
"I think that someone died, someone's in serious situation, very seriously ill, I think we did everything we can do", Marshall said.
A train carrying members of Congress to a GOP retreat struck a garbage truck in Virginia and some people are injured, according to those at the scene.
"It was an bad scene", McSally said.
U.S. Senator Bill Cassidy, a doctor, said he and other lawmakers who are physicians tended to the injured until emergency personnel arrived. Flake said another person wasn't as seriously injured, and was able to walk to the ambulance. But the extent of the damage and other injuries to those inside the truck is unclear.