(CNN) An Amtrak passenger train was mistakenly diverted to a side track and crashed into an unmanned freight train in South Carolina, killing two Amtrak employees and injuring 116 people, federal officials said.

Amtrak Train 91 was traveling south early Sunday and should have continued straight down the tracks, but the rail switch had been manually set to divert the train onto the rack where the CSX train was parked, National Transportation Safety Board Chairman Robert Sumwalt said at a news conference.

A padlock held the switch in its alignment, which is standard procedure when switches are manually operated, Sumwalt said.

"Key to that investigation is learning why that switch was lined (aligned) that way," he said.

Sumwalt said video from the front of the Amtrak train had been recovered and sent to Washington, where it will be inspected. That will help investigators determine what happened in the 2:35 a.m. collision, including whether the train braked or was exceeding the 59 mph speed limit, he said.

Engineer, conductor killed

Lexington County spokesman Harrison Cahill said 116 people were injured and transported to hospitals, with injuries ranging from scratches to broken bones.

Officials initially said 70 people with injuries were transported for treatment, but later adjusted the figure.

Killed were two Amtrak employees: train engineer Michael Kempf, 54, of Savannah, Georgia, and conductor Michael Cella, 36 of Orange Park, Florida, Lexington County Coroner Margaret Fisher said.

No positive train control

An aerial view of the site of the crash site near Cayce, South Carolina.

Sumwalt said the crash could have been avoided if positive train control -- a system that combines GPS, wireless radio and computers to monitor trains and stop them from colliding, derailing or speeding -- had been in place.

Railroad companies have until the end of 2018, and possibly two more years afterward, to implement PTC.

Sumwalt said he didn't know why this particular train didn't have PTC.

Richard Anderson, Amtrak CEO and president, told CNN's Rene Marsh that the signal system along the section of track where the crash occurred was down and the tracks were being manually controlled by CSX. Sumwalt confirmed the tracks were owned and operated by CSX.

Anderson said the CSX dispatch center directed the Amtrak train to the track where the derailment happened. The CSX dispatch center was manually directing the Amtrak train via telephone communications, Anderson said.

According to Anderson, CSX has complete control of the tracks, signals and switches in the area where the crash happened.

CSX statement

A CSX spokesperson issued this statement:

"Our sincere condolences go out to the families of the two individuals who passed away following the tragic events that took place in Cayce, South Carolina, early this morning. We remain focused on providing assistance and support to those impacted by today's incident.

"CSX hosts more passenger trains on its network than any other major railroad in the United States, and passenger rail remains one of the safest ways to travel. The National Transportation Safety Board is leading the investigation into this incident and CSX will continue working with the investigating team."

Fuel spilled

The Amtrak Train 91 was traveling between New York and Miami with a nine crew members and 147 people aboard when it collided with the CSX freight train in Cayce, derailing the lead engine and some of the seven passenger cars, Sumwalt said.

Sumwalt said the CSX train, made up of two locomotives and 34 empty cars, had just unloaded a shipment of automobiles at a nearby siding. The train was empty of people, authorities said.

About 5,000 gallons of fuel were spilled, authorities estimated, but Cahill said there was "no threat to the public at the time."

President Donald Trump has been briefed on the accident, according to a statement from White House deputy press secretary Lindsay Walters.

"My thoughts and prayers are with all of the victims involved in this morning's train collision in South Carolina," Trump wrote in a tweet on Sunday afternoon . "Thank you to our incredible First Responders for the work they've done!"

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! — Donald J. Trump (@realDonaldTrump) February 4, 2018

'Nobody was panicking'

Derek Pettaway was a passenger in one of the train's rear cars, headed for Orlando. He was awakened by the impact, and the crew came through the cars "really quickly" and got everybody off the train.

"Nobody was panicking," Pettaway said. "I think people were more in shock than anything else."

Pettaway was discharged from a hospital with minor whiplash, he said. From there, he went to a shelter at Pine Ridge Middle School for passengers who didn't suffer serious injuries.

Other Amtrak accidents

Sunday's was one of several fatal incidents involving an Amtrak train in the past few weeks.

In December, an Amtrak train derailed near DuPont in Washington state and hurtled off an overpass onto Interstate 5, killing three people. The Amtrak engineer on that train told investigators he mistook a signal and braked moments before the deadly crash , according to the National Transportation Safety Board.

A CNN investigation found that engineers and conductors had complained to supervisors that they were not adequately trained for the new route before the crash of Amtrak 501.

Last week, an Amtrak train carrying members of Congress to a Republican retreat in West Virginia struck a truck near Charlottesville, Virginia . Investigators looking into the crash are focusing on the actions of the driver of a truck, a source with knowledge of the investigation told CNN.