BRIDGEPORT, Connecticut (AP) - Tens of thousands of commuters are bracing for a difficult trip around southwest Connecticut and to New York City beginning Monday as workers repair the Metro-North commuter rail line crippled by a derailment that injured scores of passengers.

Crews will spend days rebuilding 600 metres of track, overhead wires and signals following the collision between two trains on Friday evening that injured 72 people, Metro-North President Howard Permut said on Sunday. Nine remained hospitalised.

"This amounts to the wholesale reconstruction of a two-track electrified railroad," he said.

Several days of around-the-clock work will be required, including inspections and testing of the newly rebuilt system, Permut said. The damaged rail cars were removed from the tracks on Sunday, the first step toward the repairs.

Gov. Dannel P. Malloy warned on Sunday that traffic in southwest Connecticut could be a mess for as much as a week until service is restored to the commuter rail line.

Mr Malloy even urged commuters to stay out of the state if possible.

"Tomorrow's commute will be extremely challenging," he said at a brief news conference in Hartford. "Residents should plan for a week's worth of disruptions."

Each day, approximately 30,000 Metro-North customers use the 12 stations on the New Haven line between South Norwalk and New Haven where service has been shut down, according to the Metropolitan Transportation Authority, which operates Metro-North.

If all the affected commuters took to the highways to get to work, "we would literally have a parking lot," the governor said.

The state will dispatch more state troopers and tow trucks to respond to car accidents that could come with crowded roads and slippery conditions due to a rainy weather forecast , he said.

Amtrak passenger train service between New York and New Haven also was suspended, and there was no estimate on service restoration. Limited service was available between New Haven and Boston.

About 700 people were on board the trains Friday evening when one heading east from New York City's Grand Central Terminal to New Haven derailed just outside Bridgeport. It was hit by a train heading west from New Haven.

Investigators are looking at a broken section of rail to see if it is connected to the derailment and collision.

National Transportation Safety Board investigators arrived 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, among other things.

The MTA operates the Metro-North Railroad, the second-largest commuter railroad in the US The Metro-North main lines run northward from New York City's Grand Central Terminal into suburban New York and Connecticut.

Commuter trains damaged in a crash in Connecticut were being removed on Sunday in the first step to making repairs and restoring service, the agency that runs Metro-North said.

Mr Aaron Donovan, spokesman for the Metropolitan Transportation Authority, said the National Transportation Safety Board, which is investigating the crash, gave Metro-North the OK to remove the trains. Hundreds of feet of track need to be repaired, he said.

"We have a lot of work ahead of us, to restore signals and overhead wires," Mr Donovan said.

Later Sunday, the Connecticut Department of Transportation will announce jointly with Metro-North a plan for the rush-hour commute beginning Monday.

Investigators are looking at a broken section of rail to see if it is connected to the derailment and collision outside Bridgeport that left dozens injured. Seventy-two people were sent to the hospital Friday evening after an eastbound train from New York City derailed and was hit by a westbound train. Nine remain hospitalised.

Service has been suspended between South Norwalk and New Haven, which includes stops at 12 stations.

Mr Donovan compared the loss of service to a "very significant storm."

Investigators said on Saturday that the crash was not the result of foul play, but a fractured section of rail is being studied to determine if it is connected to the accident.

National Transportation Safety Board member Earl Weener said the broken rail is of substantial interest to investigators and a portion of the track will be sent to a lab for analysis.

Mr Weener said it's not clear if the accident caused the fracture or if the rail was broken before the crash. He said he won't speculate on the cause of the derailment and emphasised the investigation was in its early stages. Officials earlier described devastating damage and said it was fortunate no one was killed.

The crash damaged the tracks and threatened to snarl travel in the Northeast Corridor. The crash also caused Amtrak to suspend its passenger train service between New York and Boston.

NTSB 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, among other things.

The MTA operates the Metro-North Railroad, the second-largest commuter railroad in the nation. The Metro-North main lines run northward from New York City's Grand Central Terminal into suburban New York and Connecticut.