A commuter train traveling eastbound from New York City derailed near the Connecticut suburb of Fairfield during the evening rush hour on Friday and collided with a westbound commuter train, injuring up to 60 people, three critically, officials said.
The collision of the two Metro North trains forced Amtrak to shut down service indefinitely between New York and Boston, the national railroad said.
Three people were critically injured and 60 people were transported to area hospitals, police said.
"It's pretty devastating damage to a number of cars," Connecticut Governor Dannel Malloy told a news conference. "These cars came into contact (and the impact) ripped open the siding of one of the cars. There is extensive damage in the front and the wheels."
The accident occurred shortly after 6 p.m. EDT (2200 GMT), authorities said.
"All of a sudden the train started to shake a little bit ... like something was bumping into it," passenger Rowana Shepherd told CBS television. "One entire compartment from the other train was completely ripped open. The whole side was gone and people were lying in between the trains."
The eastbound train was headed to New Haven, Connecticut, when it derailed and collided with the westbound train that was running to New York's Grand Central Station, said Aaron Donovan, a spokesman for the Metropolitan Transportation Authority (MTA), which runs the commuter railroad.
"The head end of both trains, the front end of both trains, collided and received sustained damage. ... But it was not a full head-on collision," Donovan said.
Metro North is a commuter railroad serving the northern suburbs of New York City. It is operated by the MTA, a New York State agency. Fairfield is about 50 miles (80 km) north of New York City.
The number of injured could rise because hospital officials were told to prepare to receive up to 180 patients total. Metro North trains can carry up to 300 passengers when full.
Thirty-three people were transported to St. Vincent's Medical Center and 27 to Bridgeport Hospital, police said.
Bridgeport Hospital had two patients with critical injuries, and the others could be described as "walking wounded" with a variety of lesser injuries, spokeswoman Anita Shrum said.
One person had serious head and neck injuries at St. Vincent's Medical Center in Bridgeport and the others had minor injuries, spokeswoman Dianne Auger said.
The cause of the derailment was not immediately known. The National Transportation Safety Board said it was sending a team of investigators to Connecticut to look into the accident.
Malloy said the collision would have a big impact on the vital rail corridor between Boston and New York City for days.
The Westport and Fairfield stations will be closed to commuter rail and Amtrak service at least through the weekend as workers repair the damage and investigators probe the derailment, he said, adding that there was no reason to believe that it was anything but an accident.