An investigation is under way after 60 people were injured when two commuter trains serving New York City collided in Connecticut during the evening rush hour.

Connecticut Governor Dannel Malloy said that five people were in a serious condition in hospital.

"It's pretty devastating damage to a number of cars," Mr 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 6pm local time (11pm Irish time).

The eastbound train was travelling 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.

"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," Mr Donovan said.

The site of the crash in Fairfield is about 80km north of New York City.

The cause of the derailment is not yet known and the National Transportation Safety Board said it was sending a team of investigators to Connecticut to look into the accident.

Mr Malloy said the collision would have a big impact on the vital rail corridor between Boston and New York City for a number of days.