Investigators on Monday were trying to determine why an Amtrak passenger train struck and killed two members of a maintenance crew on the tracks near Philadelphia, derailing the train and injuring 35 others.

The National Transportation Safety Board was analyzing an event data recorder and video recordings that were recovered after the front of the train went off the tracks in Chester, Pennsylvania, about 15 miles (25 km) southwest of Philadelphia, Sunday.

People who were aboard Amtrak Train 89, bound for Savannah, Georgia, from New York with about 330 passengers, described the jolt when the train struck a large piece of railway equipment on the tracks.

Steve Forbes, the U.S. publishing executive and two-time former Republican presidential hopeful, told CNN on Monday he was riding in the last car of the train that crashed.

"It was a matter of nanoseconds, but you felt the train was coming to a screeching halt, then it eased up a bit, then another screech," Forbes said. "There was coffee flying everywhere. There was the smell of smoke."

The locomotive engineer was among 35 people on board the train who were taken to hospitals with injuries, none of them life-threatening, the NTSB said.

Forbes said passengers determined there was no fire and decided to stay inside the train car to avoid contact with live electrical wires outside. They did not receive instructions until first responders made their way to the final car about 30 minutes later, he told CNN.

Forbes said the train's public address system apparently was disabled in the crash.

"You'd think in this day and age they would have a backup system if the electricity goes down so they can say something  like, 'Stay on the train,'" Forbes said. "We knew that already, but it's nice to hear that somebody is overseeing the thing."

Amtrak spokesman Mike Tolbert said the railroad was operating its normal schedule of train service along the busy Northeast rail corridor Monday. He referred all other questions to the NTSB, which did not immediately respond to a request for comment.

The crash was the latest in a series involving the U.S. passenger rail carrier and occurred a few miles south of the site of a 2015 derailment in which eight people were killed.