A locked switch is being blamed for the collision between an Amtrak passenger train and a freight train that killed two people and injured more than 100 others in South Carolina early on Sunday.
The head of the National Transportation Safety Board said a switch on the tracks, which the freight hauler CSX owns and operates, was padlocked in a position that steered the Amtrak train onto a siding near Columbia, S.C., where it crashed into a parked, unoccupied CXS train.
"Key to this investigation is learning why the switch was lined that way," Robert Sumwalt, the chairman of the NTSB, told reporters at a news conference on Sunday. NTSB officials were not immediately available to elaborate.
Amtrak President and Chief Executive Richard Anderson told reporters Sunday that CSX was responsible for the wreck because of the locked switch. CSX officials were not available for comment.
Officials from both companies expressed condolences to the families of the two people killed, an Amtrak engineer and a conductor.
Two of the 116 people injured remained in critical condition overnight, officials said. Specifics were not available.
A team from the NTSB is expected to be on the scene for five to seven days. No probable cause will be issued at that time, the agency told media outlets.
Robert Sumwalt, chairman of the U.S. National Transportation Board, told a news conference the section of track was operated by CSX and there was a padlock on the switch that steered train traffic onto the siding.
"Key to this investigation is learning why the switch was lined that way," he said, calling the damage to the locomotives "catastrophic." An NTSB investigation team was at the site.
Amtrak engineer Michael Kempf, 54, of Savannah, Georgia, and conductor Michael Cella, 36, of Orange Park, Florida, were killed, Lexington County Coroner Margaret Fisher told reporters. Autopsies were being conducted, she said.
Two of the 116 people injured were in critical condition after the wreck, which occurred about 5 miles (8 km) southwest of the state capital, Columbia.
"It's a horrible thing to see, to understand what force was involved," South Carolina Governor Henry McMaster told reporters. "The first engine of the freight train was torn up, and the single engine of the passenger train is barely recognizable."
Anderson said the passenger train hit the tail end of the CSX train. That train had two locomotives and 34 empty auto racks used to transport cars, the NTSB said.
The passenger train's locomotive was left lying on its side, and the first car was bent and also derailed, although it remained upright, images from the scene showed.
At least four of the freight train's cars were crumpled, looking like crushed tinfoil, but remained on the tracks.
The passenger train was part of Amtrak's Silver Star Service. Officials said some 5,000 gallons of fuel leaked as a result of the collision but that there was no threat to public safety.
U.S. President Donald Trump received regular updates on the crash while at his resort in Palm Beach, Florida. "My thoughts and prayers are with all of the victims involved in this mornings (sic) train collision in South Carolina," he tweeted. "Thank you to our incredible First Responders for the work they've done!"
McMaster said he had been told the Amtrak train was traveling at about 59 miles per hour (95 kph) on impact.
The NTSB did not release details on the speed at which the Amtrak train was traveling.
In December, three people were killed when an Amtrak passenger train derailed in Washington state. The engineer later told the NTSB he had misread a signal and tried to brake before the accident.
In late January, an Amtrak train carrying Republican members of the U.S. Congress killed one person in a garbage truck with which it collided in Virginia.
A Federal Railroad Administration Investigative team was also on the scene in South Carolina to help establish what happened.
"It is important to understand the factors that contributed to this tragic accident and how all stakeholders can ensure a safe and reliable rail system going forward," the U.S. Department of Transportation said in a statement.
A CSX spokesperson issued the following statement on the incident:
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.
—CNBC contributed to this report.