The incident happened near Lewes railway station on Thursday afternoon and involved a Southern Rail train.
Two people have been seriously injured after a train with around 150 people on board derailed near Lewes in East Sussex.
British Transport Police (BTP) declared a major incident as three carriages derailed on their side, trapping passengers on board the Southern train on Thursday afternoon.
The train, which was travelling from London Victoria to Eastbourne, has now been safely evacuated, the force said.
Outside a community centre hosting passengers nearby, Yana Ludwig, who was travelling alone on the train from London to Lewes, told reporters the experience as “completely terrifying”.
“There was a banging. Everything just went topsy turvy,” the 56-year-old from the United States said.
“It seemed like a really long time but it probably was 10 seconds of that before the carriage actually fell on the side.”
She described being propped up over the top of another passenger.
She added: “I’m pretty banged up.”
She said everyone in the train was checking their fellow passengers were OK, adding: “These moments everybody kind of pulls together.”
BTP believes that two patients have sustained serious injuries and a further nine patients have sustained less serious injuries.
“Patients have been assessed and treated at the scene, with some transported to local hospitals,” the force added.
South East Coast Ambulance Service added that a number of passengers who did not require hospital treatment have been taken to a local community centre, where they are being supported by partner agencies.
“This remains a complex and ongoing multi-agency response,” a spokesperson said.
Fire engines, ambulances and police have been stationed along Landport Road in Lewes, alongside a double decker bus was parked up by the community hub awaiting for passengers to board.
One person could be seen being taken away in an ambulance.
Local resident Oriana Evans said she and her son helped casualties who were led off the train towards the community centre along the street, showing them where to go, including some passengers who were on holiday.
“I walked and chatted to some of them in shock really,” the 54-year-old jewellery maker said.
She said they told her they were alright but “really bruised”.
Photographs circulated online show at least two carriages of a train lying on their side, with two passengers standing on top.
Transport Secretary Heidi Alexander said she is “deeply concerned” by the incident and is “working quickly with the rail industry and local partners to assist passengers”.
BTP Assistant Chief Constable Ian Drummond-Smith said: “Our thoughts are of course with everyone affected, and I’d like to reassure the public that we’re supporting the Rail Accident Investigation Branch to establish exactly what’s happened. We’ll provide further information as soon as we are able”.
