Train services out of Britain’s busiest station were suspended on Wednesday evening after man was seen chasing a dog along electrified tracks.
All lines in and out of London Waterloo were blocked at about 7pm due to trespass, South Western Railway said.
“Disruption is expected until the end of the day,” it said on Twitter.
Passengers said power had been switched off to trains on the line, which uses an electrified “third” rail.
Video shared on social media showed a man running along the tracks at the approach to the station.
“We saw a dog running down the track and then, 20 seconds later, a man running after it,” said passenger Adam Willmott, 23. “The dog was much faster and the man was looking rather tired.”
He said his London-bound train had been stationary for more than 20 minutes with no power.
“We have no air conditioning and it is just getting hotter and hotter,” he said. “The train manager said he doesn’t know when we will move.”
A spokesman for South Western Railway said: “I can confirm that the trespass incident involves an individual chasing a dog down the rail lines and that services have been held between Waterloo and Vauxhall stations. The British Transport Police have been called to handle the incident.”
It follows earlier disruption at London Euston and London St Pancras because of heat-related problems on tracks.