There were two leaks from the train, spilling an estimated 18,925 litres of fuel, but there was "no threat to the public at this time," Cahill said at a news conference. The cause of the crash is not known. He later said that it was unclear from where the fuel had leaked.
The National Transportation Safety Board and Federal Railroad Administration are both at the site to investigate the crash.
"The Federal Railroad Administration Investigative team is on site to support to the National Transportation Safety Board's investigation," the US Department of Transportation said in a statement. "We are closely monitoring the situation and have been in contact with CSX and Amtrak as well as federal, state and local officials."
The Transportation Department said Secretary Elaine Chao also is sending her senior adviser, Jim Ray, to the crash site. "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."
Amtrak said it was "cooperating fully" with the NTSB investigation.
In a statement, Amtrak said CSX owns and controls the Columbia Subdivision tracks where the crash occurred, including overseeing the dispatching of trains and signal systems. CSX's duties include "directing the signal systems which control the access to sidings and yards," Amtrak said.
US President Donald Trump offered his words of support and thanked first responders in a tweet: "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!"
This is the third crash involving an Amtrak train in less than three months. Last week, an Amtrak train carrying GOP lawmakers to a retreat in West Virginia collided with a rubbish truck. One person in the truck was killed in the crash in Crozet, Virginia. In December, an Amtrak train in Washington state derailed while crossing an overpass, spilling carriages onto a busy highway and killing three people.
Federal investigators have not determined the cause of the earlier crashes; investigations can take months or even years, but the incidents are likely to raise concerns about the safety of the nation's rail system and focus more attention on the push to install a technology known as positive train control, an automatic braking system that federal safety officials say could have prevented hundreds of deaths and thousands of injuries over the years.
Last month, Chao told railroad industry officials that they are expected to meet the deadline to have the systems installed by the end of this year.
Whitney Sullivan, a reporter for WLTX-TV, reported that deputies said no residents in the area were evacuated.
Officials from the Federal Railroad Administration, which has safety oversight over Amtrak and freight rail, said its investigators were headed to the scene.
Passenger Derek Pettaway said he woke with a jolt when the collision happened, suffering minor whiplash. He had taken shelter with other passengers at the nearby Pine Ridge Middle School, where authorities were providing medical care. "No one was panicking. I think most people were asleep. I think people were more in shock," Pettaway said in an interview with CNN.
