Passengers on a packed commuter train were forced to flee when they heard several "explosions" and saw a fire flare up alongside the carriage.
The South Western Railway service was travelling between London Waterloo and Hampton Court at around 6.30pm when witnesses reported seeing sparks and smoke.
It pulled into Berrylands station, south-west London, where commuters were told to leave the platform by emergency services.
Dramatic pictures posted on social media show flames shooting up the side of the train's front carriage.
The rail operator said it had come from a "line side fire", prompting cancellations and delays along the line.
Media Consultant Graham Lovelace, 55, was travelling home to Hampton Court when he was caught up in the scare.
He told the Press Association: "(The) train was busy, front carriages packed, passengers standing - including me.
"Just after we left New Malden station there were loud bangs and bright white sparks.
"I was in the front carriage where the electrical fault seemed to be located.
"There was a strong smell of smoke and passengers shouted to open the windows.
"Soon after there were more large sparks and more smoke.
"As the train pulled into Berrylands station people left the train, but that was when the biggest explosions happened. Everyone got off the train and stood on the platform."
Fire crews soon arrived on the scene and ordered everyone off the platform, he added.
South Western said: "We are currently in contact with the train crew, and our specialist teams will be working hard to ascertain the problem and rectify it as soon as possible to get the line reopened.
"The fire service are also on the scene to investigate the cause of the fire.
"Initial reports suggested that a train had caught fire, this has now been confirmed not have been the case."
Train services running to and from stations along the line may be delayed or revised until 10pm, according to the operator