A busy commuter train was derailed in Liverpool after a mechanical fault, trapping 119 passengers underground.
Stretchers were taken to the scene but there no major injuries
The Wirral line Merseyrail train came off the tracks in a tunnel 200m from Liverpool Central Station at 1750 BST.
British Transport Police said it happened at low speed and there were no major injuries. Two elderly people had to be treated at the scene for shock.
Emergency services helped passengers off the train five at a time and all were led to safety within two hours.
A passenger on the train, who gave his name as David, said of Wednesday's derailment: "There were a few judders and the train came to a stop.
"All the lights went out and it went dark."
"There were a few people upset but we all kept calm. A few kids were crying.
"It's quite scary with the terrorist alerts. I'm sure I wasn't the only one thinking it was a terrorist thing.
"We were taken off five at a time because we had to make our way through the tunnel and there were a lot of obstacles like cables and holes. It was pretty well organised."
Another passenger, who gave her name as Mary, said: "The train just started going crazy.
"It was just jolting everywhere. We didn't know what was happening. It was very scary."
"When the train did stop we were very grateful that we were safe."
"I didn't see anybody come off their seats but it was jolting about a lot and finally stopped."
Local officials of the train driver's union Aslef said there was a temporary speed restriction of 20mph in the section of the tunnel where the derailment took place.
The union was sending its own health and safety experts to the scene to help with the evacuation of passengers.
Alex McDougall, of Merseyside Fire and Rescue, said it was "extremely dark and unpleasant" in the tunnel.
Peter Mulcahy, incident commander for Mersey Regional Ambulance Service, said: "Looking at the passengers they were very spirited when they came off the train.
"Some people were quite upset and shocked but a lot of people just wanted to get on with their normal business and make their way home."
A spokesperson for Merseyrail, which operates Liverpool's underground service, said the emergency procedures had worked and a full investigation into the cause of the derailment would take place.
'Good safety record'
Merseyrail said all trains from the Wirral were now being turned back at James Street station, rather than going around the loop of the city.
Local bus services were taking people into the city centre instead.
Louise Ellman, Liverpool Riverside MP, said: "Merseyrail have a very good record in terms of safety but this is very frightening and I hope there are not any serious injuries.
"The system is a very popular one and it has a good record. It recently had more investment and in my view it's a model system."