Hundreds of passengers have been left stuck for more than four hours on several South West Trains services outside London.
The trains stopped near Woking after leaving Waterloo on Thursday evening.
Network Rail said an attempted cable theft was likely to be the reason for the problem.
But it said further delays were caused when passengers on stationary trains went on the track, meaning power to the rails had to be turned off.
One passenger, who asked only to be named as Keith, said he took the 18.33 South West Trains service from Clapham, which ground to a halt near Woking.
“When we got to the gates the police tried to get our names, saying we were trespassing”
Keith
He described how after about two hours, he and some other passengers decided to get off the train.
“There were constant announcements every five minutes from the train driver saying he did not know when we would be moving.
“There was a lady on the train who was eight months pregnant and a man who was diabetic and needed his insulin.
“There was about five of us and we decided to get off. We prised the door open and jumped. We then walked to the station where police helped us to cross the lines safely.
“When we got to the gates the police tried to get our names, saying we were trespassing and that South West Trains take this behaviour very seriously.
“They didn’t manage to get any of our names in the end. I got home at around 23.30.”
A passenger on another train, James Bilderbeck, 39, from Basingstoke, told BBC News that the service he was on was stuck for more than four hours.
“It’s a really miserable environment, stuck going nowhere. It’s a distressing situation for all.”
The company director described it as the worst delay he had ever known as a commuter.
Speaking at about 2330 BST, he said his train had finally got moving again and that he hoped to reach Basingstoke soon.
But he said that some passengers whose final destination was Weymouth could expect for their journeys to take up to seven hours.
A South West Trains spokeswoman said: “A major signalling problem in the Woking area is currently causing disruption to South West Trains services.
“As a result, there are lengthy delays of up to two hours on all services through Woking, which is causing severe disruption to mainline services in and out of Waterloo Station.
“We would like apologise to passengers for the significant disruption and the inconvenience this will have caused.”
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