Passenger Bradley Agar of Westport, Conn., said he was in the first car of the westbound train when he heard screaming and the window smash behind him.
"I saw the first hit, the bump, bump, bump all the way down," he said.
Agar had returned to work this week for the first time since breaking his shoulder in January. And since he was still healing, he thought it would be safer to take the train than drive.
The Metro-North Railroad, a commuter line serving the northern suburbs, described it as a "major derailment." Photos showed a train car askew on the rails, with its end smashed up and brushing against another train.
Malloy said there was extensive damage to the train cars and the track, and it could take until Monday for normal service to be restored. He said the accident will have a "big impact on the Northeast Corridor."
Bridgeport Mayor Bill Finch said extra buses will be deployed, but the disruption caused by the train accident could cost the region's economy millions of dollars.
"A lot of people rely on this, and we've got to get this reconnected as soon as possible," Finch said.
The area where the accident happened was already down to two tracks because of repair work, Malloy said. Crews have been working for a long time on the electric lines above the tracks, the power source for the trains. He said Connecticut has an old system and no other alternate tracks.
By late evening, Bridgeport Police Chief Joseph Gaudett said everybody who needed treatment had been attended to, and authorities were beginning to turn their attention to investigating the cause.
"Everybody seemed pretty calm," he said. "Everybody was thankful they didn't get seriously hurt. They were anxious to get home to their families."
The Metropolitan Transportation Authority operates the Metro-North Railroad, the second-largest commuter railroad in the nation. The Metro-North main lines — the Hudson, Harlem, and New Haven — run northward from New York City's Grand Central Terminal into suburban New York and Connecticut.