An Amtrak passenger train crashed into a parked freight train in the early-morning darkness on Sunday after a thrown switch sent it hurtling down a side track, US authorities said.

Two Amtrak crew members were killed and more than 100 people were injured.

It was the third deadly crash involving Amtrak in less than two months.

The Silver Star, en route from New York to Miami with nearly 150 people aboard, was going an estimated 59mph when it struck the empty CSX train at around 2.45am, Governor Henry McMaster said.

The crash happened near a switchyard about 10 miles south of Columbia, Sout Carolina, where trains hauling cars are loaded and unloaded.

Robert Sumwalt, chairman of the National Transportation Safety Board, said investigators found a switch had been set in a position that forced the Amtrak train off the main track and ont o the siding. He said the question for investigators is why that happened.

Amtrak president Richard Anderson appeared to point the finger at CSX, saying the signal system run by the freight rail company at that spot was down at the time, and CSX dispatchers were manually routing trains. 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.

Investigators recovered a camera from the front of the Amtrak train and were looking for the data recorders from the two trains.

The switch that triggered the crash was padlocked in position, which conductors are supposed to do when they move a train from one line to another, Mr Sumwalt said.

The conductor and engineer aboard the Amtrak locomotive were killed and 116 people were taken to four hospitals, according to the governor.

At least three patients were hospitalised in critical or serious condition, with nearly all the rest treated for minor injuries such as cuts, bruises and whiplash.

Palmetto Health emergency room doctor Eric Brown said so many passengers were hurt that they were brought in on two buses, and a tent that had been set up as a waiting room to keep people separate from flu patients was turned into a triage area.

The locomotives of both trains were left crumpled, the Amtrak engine on its side. One carriage in the middle of the Amtrak train was snapped in half, forming a V off to one side of the tracks.

“It’s a horrible thing to see, to understand the force involved,” the governor said after touring the scene.

Train Crash South Carolina
South Carolina Governor Henry McMaster (Jeff Blake/AP/PA)

In a statement, Amtrak said that it was “deeply saddened” by the deaths and added that it was cooperating fully with the NTSB, as did CSX. But Amtrak also also said CSX maintains all the tracks and signals where the accident happened and controls access to the sidings and yards.

Mr Anderson said the crash shows the importance of making sure that positive train control is installed on every train and track in the nation by the government’s year-end deadline.

The system is in place in the north east, but railroads that operate tracks used by Amtrak elsewhere in the US have got extensions to the deadlines.

Amtrak officials gathered up luggage and other belongings and within hours put passengers aboard buses to their destinations. Many of them were asleep when the crash happened.

Before being sent on their way, those who were not hurt were taken to a shelter set up at a middle school, and local businesses provided coffee and breakfast.

“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,” sheriff’s spokesman Adam Myrick said.

The dead were identified as engineer Michael Kempf, 54, of Savannah, Georgia, and conductor Michael Cella, 36, of Orange Park, Florida.