Amtrak said in a statement that the collision occurred at 11:20 a.m. ET in Crozet, Virginia, after the train departed from Washington, D.C.
A number of the politicians on the train tweeted that they were OK, which was echoed by the White House.
WATCH: ‘They’re doing pretty good’: Trump reacts to Virginia train crash carrying GOP Congress members
“There are no serious injuries among members of Congress or their staff,” White House spokesman Sarah Sanders said.
One occupant of the truck died. Amtrak says two crew members and two passengers on the train sustained minor injuries.
WATCH: GOP members use medical training to help victims of train crash
The incident left authorities on high alert. Immediately after the crash, a law enforcement team dressed in black surrounded the train with automatic weapons drawn and searched the surrounding area for possible attackers as first responders treated the injured, a local emergency worker told Reuters, speaking on condition of anonymity.
“They surrounded the train on both sides and set up a perimeter with their automatic weapons pointing out and then searched the woods around the train,” the worker said.
Meanwhile, a number of the representative assisted with the injured.
WATCH: Garbage truck demolished after collision with train carrying GOP members in Virginia
“At least five members of Congress helped firefighters and EMTs (emergency medical technicians) treat the three injured people who had been in the truck,” the emergency worker said.
Rep. Chuck Fleischmann, who tweeted Wednesday that he was on the train, was also on the field last year in Virginia when a gunman opened fire on a GOP baseball practice in which Steve Scalise was badly injured.
After the train collision, Fleischmann tweeted he was “shaken up.”
The members of Congress were headed to an annual retreat in Greenbrier, West Virginia.
The policy retreat is scheduled to last three days and feature speeches from President Donald Trump and Vice President Mike Pence. By early afternoon, lawmakers were boarding buses to resume their trip and Pence was still planning to address them later Wednesday.
Pictures from the scene show a large, badly-damaged truck surrounded by debris. Law enforcement officials are on the scene investigating.
Amtrak said the train is being inspected for damage.
With files from Reuters and the Associated Press.