"The car was shaking from side to side and I could tell something was going off the tracks," Ian Turpin, 24, from Brooklyn, New York, told ABC News.
Then the train screeched to a halt, he said.
Train 55 -- the Vermonter -- was traveling from St. Albans, Vermont, to Washington, D.C., when it derailed after striking a rock slide on the tracks, Amtrak said.
Seven people were injured, the Federal Railroad Administration said. One crew member suffered serious injuries while two crew members and four passengers had non-life-threatening injuries, according to the FRA. Amtrak said the four hospitalized passengers have since been released.
A total of five passenger cars and the engine derailed, officials said. The train was carrying 98 passengers and four crew members, the FRA said.
"The preliminary cause of the accident is a rock slide in the path of the train," the FRA said, adding that a full investigation will be conducted to find the official cause.
Gov. Peter Shumlin said the rail is safe, calling the Vermonter "a great train line." Officials said there was no reason to believe there was any negligence; the track was recently rebuilt and state of the art.
The track is owned and maintained by the New England Central Railroad, Amtrak said. Michael Williams, spokesman for the New England Central Railroad and its parent company Genesee & Wyoming Inc., told ABC News that "as with all such incidents, there will be a full investigation to determine any learnings that could help prevent future incidents."
This accident comes just five months after an Amtrak train derailed near Philadelphia, killing eight people.