Tony Phillips, an advertising company employee on his way home to Stoughton, told The Boston Globe that all standing passengers fell to the floor.

"We knew we were coming into Canton Junction and suddenly the train stopped," Phillips said. "All the sudden, there was a bang, a huge explosion. People were screaming 'Oh my God, what happened?'"

Paul MacMillan, acting police chief with the Massachusetts Bay Transportation Authority, said the freight car, which had no engine attached, came loose and rolled for three miles before striking the local train to Stoughton, which had left South Station with about 300 passengers. CSX, which owns the freight car, said it was parked at a "customer location."

So many people were hurt that some of them were taken to hospitals by bus because all available ambulances were in use.

None of the injuries were believed to be life-threatening. But witnesses described people with broken noses and local residents said they saw passengers looking dazed in the woods next to the rail line.