About 60 people were injured when two commuter trains collided in Bridgeport, Connecticut, halting Amtrak service between New York and Boston in one of the worst US rail accidents since 2008.
Connecticut Governor Dannel Malloy said five people suffered critical injuries while most of the other injuries were minor.
The Metropolitan Transportation Authority, which runs the Metro-North service, said a train bound from New York to New Haven derailed about 6.10pm local time near a highway overpass in Bridgeport.
A train coming in the opposite direction on an adjacent track then struck the derailed train, the MTA said.
About 700 people were aboard the two trains when they collided, the MTA said. The accident prompted an indefinite suspension of Metro-North service in Connecticut between the South Norwalk and Bridgeport stations.
Lola Oliver, 49, of Bridgeport, a passenger on one of the trains said the crash threw her from her seat.
"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. And I just gripped it because I felt the train sliding," she said. "It happened so fast I had no idea what was going on. All I know is we crashed."
Oliver, a cardiology technician, was treated at a hospital for cuts and bruises and released.
The US National Transportation Safety Board was sending a team to the site to investigate the cause of the crash, Nicholas Worrell, a spokesman, said. Investigations usually take at least several months.
"I thought there was a bombing," said Natalie Sepulveda, 23, who was aboard the westbound train with her two-year-old son.
"I smelled smoke and looked outside the window and saw a whole bunch of dust, and I grabbed my son."
It was not immediately clear what caused the derailment.
The transportation authority said the collision occurred in an area where two of the four tracks were out of service for work on overhead wires.
Passengers recalled a chaotic scene after the crash, as passengers tried to help one another out of the train. Firefighters placed stepladders beneath the train doors to allow passengers to exit.
Andrea Turner, 26, said she was on the eastbound train.
"We were just riding along fine," she said. "We felt like the brakes were pumping, and we felt a crash."
The incident, about 80 kilometres from midtown Manhattan, caused seven of eight cars on the eastbound train to derail, as well as the first car on the westbound train. Both trains remained upright.
New York Governor Andrew Cuomo spoke to Governor Malloy to discuss their two states' efforts in co-ordinating a response to the wreck, the MTA said.
The crash may be the worst heavy-rail accident involving a passenger train in the US since a 2008 head-on crash between a Union Pacific freight train and a Los Angeles Metrolink commuter train that killed 25 people. A collision between two subway trains in Washington in 2009 killed nine people and injured dozens.
Railways have sought an extension to a 2015 deadline for installing accident-avoidance technology on passenger lines and tracks where hazardous materials are moved.
Associated Press, Bloomberg, McClatchy Tribune