-- A train carrying Republican members of Congress to a legislative retreat slammed into a garbage truck in western Virginia Wednesday morning, killing at least one person and injuring at least five others.
The deadly crash occurred in Crozet, Virginia, about 15 miles west of Charlottesville as the group headed to The Greenbrier resort in West Virginia.
NTSB investigators at the scene Wednesday night said they expect to recover two data recorders from the train.
Board Member Earl Weener confirmed the NTSB was treating the incident as an "accident," responding to reporter questions about whether it could have been an intentional act targeting GOP lawmakers. "If we find anything that indicates that this was intentional, we will turn that over to the FBI," he said.
Lawmakers were taken the rest of the way to the resort by bus and Wednesday night, House Speaker Paul Ryan, who had been on the train, told them, "I know we're all a little shaken up by what happened today."
"It just sometimes reminds you how fragile life can be," Ryan said.
Rep. Bruce Westerman, R-Ark., was on board and said he knew the seriousness of the violent crash right away.
"I’m an engineer so I know when you feel something that’s got as much mass as a train, anything you hit that causes you to feel it on the train, you know it’s a pretty significant collision,” he said.
Rep. Neal Dunn, R-Fla., echoed that sentiment, saying it didn't take long to figure out something was wrong.
"You couldn’t miss this crash. This was a huge trash truck. We hit this thing and you knew you hit something you just weren’t sure what," Dunn told ABC News.
Some members of Congress and their spouses who are doctors assisted in the rescue efforts. Dunn said there were up to 10 medically-trained lawmakers headed to the conference.
"We jumped off the train and went to work," he said. "Every member of the 'Doc Caucus' got out of the train and helped the guys who'd been injured," he said, referring to the self-titled group of doctors who are now working in Congress.
Dunn said the doors were locked but another congressman who was an Army Ranger "knew how to unlock the door and he got us out.”
Westerman praised the heroic efforts of his fellow lawmakers.
“Even before the emergency services got here, there were people off the train trying to administer first responder aid to those who were injured,” Westerman said.
The White House said in a statement that President Donald Trump had been briefed on the accident all morning. Later, in the Oval Office, he said the accident was "very sad."
"The train accident was a tough one, and a tremendous jolt," Trump said, adding the members of Congress were still "going on to the conference."
"I'll be going tomorrow and we'll be together, but it was pretty rough hit. That's what they all tell me," he said, adding that he spoke to "a few of the folks" on the scene.
Sen. Bill Cassidy, R-La., tweeted that "there were three people inside the truck that was straddling the track and which the train hit." He confirmed that one person died and wrote that one person had minor injuries and another had serious injuries.
Dunn said that the person who died in the crash "was already passed out when we got to him."
Rep. Dan Donovan, R-N.Y., told ABC station WABC that the person who died was inside the truck.
The University of Virginia Health System said Wednesday evening that six patients were transported to UVA Medical Center. One of the patients was listed in critical condition, one was in good condition, one was released, and three were still being evaluated as of 5 p.m.
Rep. Jason Lewis, R-Minn. was transported to a hospital and released after being evaluated for a concussion, according to an aide in his office. An aide tweeted Lewis would take part in the retreat.
Westerman and Rep. Ralph Norman, R-S.C., who was also on the train, said the impact severed the truck in half and sent the front of the train off the tracks. They estimated the train -- which didn't appear to brake upon impact -- to be traveling about 50 miles an hour when it struck the truck.
As ABC News was talking to Westerman, a first responder was walking through the car where he was still sitting, asking: “Is everybody OK?”
“To look out the window and see the debris and the garbage truck, I knew there were probably people injured. My thoughts and prayers are with the ones who are on the truck and our families,” he said.
The NTSB said Wednesday afternoon that it was "gathering information" about the cause of the collision, which was not immediately known. The identity of the person who died has not yet been released.
Amtrak added in a statement that two of its crewmembers and three passengers were among those injured.
The GOP later resumed its schedule. Vice President Mike Pence addressed the gathering at 7 p.m. and said he was in the oval office with the president when they heard the news.
"We were both deeply troubled at the initial reports but quickly relieved that the scope of the accident was not larger," Pence said.
President Donald Trump is scheduled to give remarks to the group on Thursday.
ABC News' Erin Dooley and Stephanie Ebbs contributed to this report.