TWO people were killed and 116 were injured after an Amtrak train slammed into a parked freight train in the US state of South Carolina.

The accident happened in the early-morning darkness Sunday after a thrown switch sent it hurtling down a side track, authorities said. Two Amtrak crew members were killed, and 116 passengers were injured.

It was the third deadly wreck involving Amtrak in less than two months, according to Canada's CTV.

The Silver Star, en route from New York to Miami with nearly 150 people aboard, was going an estimated 59 mph when it struck the empty CSX train around 2:45 am, Governor Henry McMaster said.

The crash happened near a switchyard about 10 miles (16 kilometres) south of Columbia where railcars hauling automobiles are loaded and unloaded.

Chairman of the National Transportation Safety Board (NTSB), Robert Sumwalt, said investigators found a track switch had been set in a position that forced the Amtrak train off the main track and onto the siding.

He said the question for investigators is why that happened.

Amtrak President Richard Anderson pointed the finger at CSX, saying the signal system along that stretch is run by the freight railroad but was down at the time of the wreck, forcing CSX dispatchers to route trains manually. The NTSB said it was working to confirm that.

CSX issued a statement expressing condolences but said nothing about the cause of the accident.

Mr Sumwalt said that positive train control - a GPS-based safety system that can automatically slow or stop trains - could have prevented the accident.

"That's what it's designed to do," he said, referring to technology that regulators have been pressing for for decades with mixed success.

Last Wednesday, a chartered Amtrak train carrying Republican members of Congress to a retreat slammed into a garbage truck in rural Virginia, killing one person in the truck and injuring six others.

And on December 18, an Amtrak train ran off the rails along a curve during its inaugural run near Tacoma, Washington, killing three people and injuring dozens. It was going nearly 80 mph, more than twice the speed limit.

With the recent string of crashes, "it's becoming almost like an epidemic for Amtrak," said Najmedin Meshkati, a University of Southern California engineering professor who has studied positive train control.

Positive train control is in place in the Northeast, but railroads that operate tracks used by Amtrak elsewhere in the US have won repeated extensions from the government. The deadline for installing such equipment is now the end of 2018.