An Amtrak passenger train slammed into a freight train parked on a side track in South Carolina early Sunday, killing two Amtrak employees and injuring more than 110 people, authorities said. It was the third deadly wreck involving Amtrak in less than two months.

The Silver Star was on its way from New York to Miami with nearly 150 people aboard around 2:45 a.m. when it plowed into the CSX train loaded with automobiles at an estimated 59 mph, South Carolina Gov. Henry McMaster said. The crash happened near a switchyard about 10 miles (16 kilometers) south of Columbia where autos are loaded and unloaded from railcars.

"The CSX was on the track it was supposed to be on," while the question for investigators is how the Amtrak train ended up on the side track, McMaster said.

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

The only way the Amtrak train could have gotten onto the siding was for a switch to have been thrown, Anderson said.

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

The National Transportation Safety Board sent investigators to the scene.

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.

The conductor and engineer aboard the Amtrak locomotive were killed, the coroner's office said. McMaster said 116 people were taken to four hospitals.

The main trauma hospital in the area had three patients in critical or serious condition, with the rest treated for minor injuries such as cuts, bruises and whiplash, said Dr. Steve Shelton, Palmetto Health director of emergency preparedness.

Officials have not confirmed if any New Yorkers were on the train.

Amtrak set up a passenger information line at 1-800-523-9101.

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 car 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,'' McMaster said after touring the scene.

Many passengers were asleep with the train began shaking violently and then slammed to a halt, passenger Derek Pettaway told CBS.

"You knew we'd hit something or we'd derailed,'' he said.

Elliot Smith told The State newspaper of Columbia that he was staying with a friend when they heard what sounded like a propane tank exploding.

"The sound was so loud, you instantly knew it was bad,'' he said. Smith said he and his friend saw passengers limping along the tracks, while others tried to get everyone out of the cars.

Amtrak's Anderson said the crash shows the importance of making sure that positive train control — GPS-based technology that can prevent accidents by automatically slowing or stopping locomotives — is installed on every train and track in the nation by the government's end-of-the-year deadline.

The system is in place in the Northeast, but railroads that operate tracks used by Amtrak elsewhere in the U.S. have gotten extensions to the deadlines.

Amtrak officials gathered up luggage and other belongings and within hours put passengers aboard buses to their destinations. Before being sent on their way, those who were not hurt were taken to a shelter, 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.

Lexington County Coroner Margaret Fisher's voice caught as she released the names of the dead. "Any time you have anything that happens like that, you expect more fatalities. But God blessed us, and we only had the two,'' Fisher said.

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

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

After the latest crash, Democratic Sen. Richard Blumenthal of Connecticut said the nation's railroads must be made safer, declaring, "Business as usual must end.'' He said proven technology, including positive train control, cannot continue to be delayed.

The latest wreck again raised criticism about the safety culture of the nation's passenger railway.

With the 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.

The worst rail tragedy in recent South Carolina history took place in 2005 when a freight engineer parked a train on a side track near a textile mill in Graniteville and forgot to flip the switch back to keep trains on the main track.

A freight train passing through went barreling down the side track and slammed into the parked train, killing nine people, most of them millworkers choked by chorine gas that leaked from a damaged tanker car.

National Transportation Safety Board Chairman Robert Sumwalt says the key to the investigation into a fatal Amtrak train crash will be why a switch was turned to force the passenger train onto a side track and into a parked freight train.

Sumwalt said at a news conference Sunday afternoon that the switch was padlocked to send trains on the main line to the side track, which conductors are supposed to do when they change lines.

He says the freight train crew took the CSX train from one side track across the main line and back to another side track after unloading automobiles.

Sumwalt says investigators don't know if the signals further up the line indicated the track had been switched off the main route.