NORTHFIELD, Vt. » An Amtrak train headed from Vermont to Washington, D.C., on Monday hit rocks that had fallen onto the track from a ledge, spilling the locomotive and a passenger car down an embankment, derailing three other cars and injuring seven people, authorities said.

The Vermonter train, carrying 98 passengers and four crew members, derailed around 10:30 a.m. in Northfield, 20 miles southwest of Montpelier, they said.

"This was a freak of nature," Gov. Peter Shumlin said.

One of the injured people was airlifted to a New Hampshire hospital and was evaluated in its emergency room. The six others went to a local hospital with injuries including neck, back and shoulder pains and lightheadedness.

Amtrak said a crew member was hospitalized with non-life-threatening injuries but four other people were released by Monday evening.

Passenger Bob Redmond, of Bay City, Michigan, was taking a foliage tour and sitting in the front row of the third car when the train derailed. He looked outside the window and saw the car that had been ahead of his was now alongside him.

"It was just going the other way, and we started tipping sideways and down we went," he said.

The National Transportation Safety Board was investigating. It was sending a small team rather than the full-blown effort made for a fatal Amtrak derailment in Philadelphia in May.

The track where Monday’s crash occurred had been part of a $220 million upgrade of New England Central Railroad tracks. In early 2013, after the upgrade had been completed, the speed limit in the area was increased from 55 mph to 59 mph.

Shumlin said there was no reason to believe there was any negligence on anyone’s part.

"We don’t have all the details, but this track was rebuilt, it was state-of-the-art track," he said. "Ledge slides happen."

Federal records show New England Central Railroad, which operates that stretch of tracks, has had four accidents since 2006 that could have involved track debris. The company was bought by Genesee and Wyoming Railroad in 2012, and of 54 total accidents that involved the railroad since 2006, six occurred under the new management, Genesee & Wyoming Inc. spokesman Michael Williams said. Of three people who died in accidents involving the railroad, two were trespassers and one was in a grade crossing accident.

Federal safety rules for tracks that carry passengers require at least two inspections every week, with at least one day between inspections.

State officials said a freight train passed over the tracks Sunday night with no problems.

When asked if there was technology available that could have detected the slide before the train went through, officials said no.

"There is not really anything that’s going to detect this kind of thing," said Vermont Agency of Transportation rail chief Dan Delabruere.

Numerous derailments worldwide have been caused by track debris, many linked to heavy rains that trigger slides or heavy winds that knock down trees. In 2010, a train in Beijing hit mounds of debris on the track following a landslide, killing 19 people.

The region near Monday’s derailment received 2.5 inches of rain between Thursday and Friday.

The Vermonter takes the route daily, beginning in northern Vermont. The 13-hour, 45-minute trip leaves St. Albans, Vermont, at 8:58 a.m. then passes through Springfield, Massachusetts, and New York, with D.C. as the destination.

Three cars that left the track Monday remained upright. Rail company officials confirmed details of the crash but did not immediately provide a comment.

Tracy Zaplitny, also of Bay City, said she and other passengers broke a window to get out of the train.

"It’s a huge wreck up there," she said.

At least several dozen passengers were loaded onto school buses to be taken to an armory at nearby Norwich University. Passengers helped each other after the crash.

The clearing of the track was to begin immediately, although officials did not know how long it would take before the section is reopened. Amtrak planned to bus passengers booked on the Vermonter to and from Springfield.

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Associated Press writer Joan Lowy contributed to this report from Washington, D.C.