Officials described a devastating scene of shattered cars and other damage where two trains packed with rush-hour commuters collided in Connecticut on Friday night, saying Saturday that it was fortunate no one was killed and there were not even more injuries.

Seventy-two people were sent to the hospital after the crash, which damaged the tracks and threatened to snarl travel in the northeast corridor.

"The damage is absolutely staggering," said Senator Richard Blumenthal, describing the shattered interior of cars and tons of metal tossed around. "I feel that we are fortunate that even more injuries were not the result of this very tragic and unfortunate accident." Senator Chris Murphy echoed that, saying it was "frankly amazing" people had not been killed. Both said the new train cars built with higher standards may have saved lives.

Governor Dannel P Malloy couldn't say when Metro-North Railroad service would be restored. The crash also caused Amtrak to suspend service between New York and Boston. Malloy said commuters should make plans for alternative travel through the area and urged them to consult the state Department of Transportation website for information. "I think this is going to be with us for a number of days," the governor said.

National Transportation Safety Board investigators arrived on Saturday and are expected to be on site for seven to 10 days. They will look at the brakes and performance of the trains, the condition of the tracks, crew performance and train signal information, and other factors. A NTSB board member, Earl Weener, said he would not speculate on a cause for the collision. He said data recorders on board were expected to provide the speed of the trains at the time of the crash and other information.

"Our mission is to understand not just what happened but why it happened and determine ways of preventing it from happening again," Weener said. Asked if there were any signs of foul play and if investigators could rule out any cause, Weener said: "It's too early to rule out anything. We just got on scene. That, of course, will be something we look at immediately."

Blumenthal referred to the crash as an accident and Malloy said on Friday there was no reason to believe it was anything other than that. About 700 people were on board the Metro-North trains when one heading east from New York City's Grand Central Terminal to New Haven derailed at about 6.10pm, just outside Bridgeport, transit and Bridgeport officials said. Passengers described a chaotic, terrifying scene of crunching metal and flying bodies.

"All I know was I was in the air, hitting seats, bouncing around, flying down the aisle and finally I came to a stop on one seat," said Lola Oliver, 49, of Bridgeport. "It happened so fast I had no idea what was going on. All I know is we crashed."

The train was hit by a train heading west from New Haven to Grand Central on an adjacent track, said a Metropolitan Transportation Authority spokesman, Aaron Donovan. Some cars on the second train derailed as a result of the collision. A spokeswoman for St Vincent Medical Center said 46 people from the crash had been treated there, and that six of those were admitted. All were in stable condition, she said. A Bridgeport Hospital spokesman said 26 people from the crash had been treated there, with three of them admitted. Two were in critical condition and one was in stable condition, he said. The other 23 were released.

Malloy said there was extensive damage to the train cars and the track. He said the accident will have a "big impact on the northeast corridor".

Bridgeport's mayor, Bill Finch, said the disruption caused by the crash 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.

Passenger Bradley Agar 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.

The area where the crash 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. Malloy said Connecticut has an old system and no other alternate tracks.

The MTA 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 Grand Central, into suburban New York and Connecticut.