Gov. Dannel P. 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.
Weener said data recorders on board are 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.
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 6:10 p.m. just outside Bridgeport, transit and Bridgeport officials said. Passengers described a chaotic, terrifying scene of crunching metal and flying bodies.
A spokeswoman for St. Vincent Medical Center said late Saturday that 46 people from the crash were treated there, with six of them admitted. All were in stable condition, she said.
A Bridgeport Hospital spokesman said 26 people from the crash were treated there, with three of them admitted. One was in critical condition and two were in stable condition, he said. The other 23 were released.
Bridgeport Mayor Bill Finch said the disruption caused by the crash could cost the region's economy millions of dollars.
Passenger Frank Bilotti said he was returning from a business trip in Boston on the westbound train when it crashed.
"Everybody was pretty much tossed around," said Bilotti, 53, of Westport, who wasn't injured other than a sore neck.
Firefighters used ladders to help people evacuate after the derailed cars dug into the banks of the tracks, Bilotti said.
"There were people on stretchers," he said. "There were people lying on the ground."
Blumenthal credited first responders, saying their "quick reactions and heroic efforts undoubtedly saved lives."
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 New York City's Grand Central Terminal into suburban New York and Connecticut.
At Grand Central, Frances Liu and her family were trying to get to New Haven, where Liu is graduating from Yale. A train could get them only as far north as Stamford.
"And then we'll rent a car and drive," she said.
Liu's parents had flown in from China for her graduation and were touring the country around her commencement. But the car-rental plan could face a snag — Liu never got a driver's license, although her parents had their Chinese licenses.
"My mom can drive. So I hope it'll be OK!" Liu said as she rushed off to decide on a train.
The last significant train collision involving Metro-North occurred in 1988 when a train engineer was killed in Mount Vernon, N.Y., when one train empty of passengers rear-ended another, railroad officials said.
Associated Press writers Michael Melia in Hartford, Conn., Susan Haigh in Fairfield, Conn., and Verena Dobnik in New York City contributed to this report.