AMTRAK, the main passenger rail service in the US, was under mounting pressure yesterday after two of its employees were killed and 116 passengers injured when a train hit a stationary freight train - the second deadly incident involving the company in a week.

The accident happened on Sunday about 2.45am local time close to Columbia, South Carolina.

Images showed the front Amtrak engine and that of the freight train wrecked and strewn by the sides of the track.

As it was announced the FBI was helping local police in documenting the scene of the incident, the National Transportation Board said it was launching an investigation.

South Carolina Governor Henry McMaster told reporters it appeared the freight train, owned by CSX, was not moving and had no people on board.

"It appears to me that the CSX train was on the track it was supposed to be on. It appears Amtrak was on the wrong track,” he said.

"I think it will prompt a new conversation around the country. We just cannot have these accidents. We go to great pains to make sure these things do not happen, but occasionally they do.”

Amtrak engineer Michael Kempf, 54, and conductor Michael Cella, 36, were killed.

"When you consider a train that size and how many people were on board, you would expect more fatalities,” Lexington County coroner Margaret Fisher said.

She said she had been speaking to the men's relatives. "They are very distraught, very shocked, as anybody would be in this situation. We are working with them to make sure they are taken care of.”

Transportation official Tom Allen told The State a switching issue probably caused the Amtrak train to run onto the side track.

"Part of the preliminary indications are that it would have to be a switching issue,'' he said. "It was no derailment caused by a flaw in the track. The Amtrak was on the wrong track.''

It is the third deadly accident involving Amtrak, which is partly owned by the US government, in less than two months.

Last Wednesday, a train carrying Republican members of Congress hit a truck carrying garbage in Virginia, killing a passenger in the truck.

In December, an Amtrak train going more than twice the speed limit ran off the rails while travelling on a new route near Tacoma, Washington killing three and injuring dozens.

Associated Press said the latest incident happened near a rail yard about 15km south of Columbia, where several track spurs split off for freight cars to be unloaded.

Amtrak officials worked to gather luggage and other belongings and line up buses to take passengers on to their destinations. Those who were not hurt were taken in patrol cars to a shelter, and local businesses stepped in to provide drinks and meals.

"We know they are shaken up quite a bit. We know this is like nothing else they have ever been through. So we wanted to get them out of the cold, get them out of the weather - get them to a warm place,” said sheriff's spokesman Adam Myrick.

President Donald Trump said on Twitter: "My thoughts and prayers are with all of the victims involved in this mornings train collision in South Carolina. Thank you to our incredible first responders for the work they've done.”

Yet others pointed out the pressing need for what they said was a failing infrastructure. Amtrak is partly owned by the US government.

Lawrence Summers, a Harvard economist who served as director of Barack Obama's National Economic Council, said: "Third major Amtrak accident in two months. Constant infrastructure breakdowns. Rising death rates for the middle aged. USA showing symptoms, like USSR in 1980s, of decay. This, not demonising FBI, should be focus of President Donald Trump and government.”