Passengers were left on a train stranded between two stops for 90 minutes after reports a power rail was ripped off the track.
All services along the First Capital Connect loop heading north between Sutton and Streatham are suspended until further notice, but services between Streatham and Sutton via Hackbridge have reopened.
The train, the 11.28am service to Bedford, stopped a mile outside Tooting just after noon today. It is still on the track.
A passenger, who gave his name as Keith, launched a scathing attack on the response from rail staff, though praised the train driver for his actions.
He said: "It took them an hour and a half to get us out. There were people here with flights, heading to appointments, one to an interview. It took an hour even for them to bring up the correct type of stepladder. The driver though was extremely good."
He described how they walked across the tracks and were able to exit the tracks at a maintenance access.
Passengers at Wimbledon Station were also left sitting on a train at Platform 9 for 30 minutes before being told to get off the train and make other arrangements.
A spokesman for First Capital Connect said: "The priority when things like this happen is to make sure passengers are safe, and the safest place for them to be is on the train.
"Before we evacuate we have to turn off power to the lines and this can take time. I apologise to people who had to wait but we always work with their safety as the top priority."
While the power was off all routes north and south were suspended.
First Capital Connect have been unable to give a time when the full service will resume.
As a result the operators have arranged for a coach to visit Rutlish School, by Wimbledon Chase station, which will be taking pupils who usually use the loop to relevant stations as far as Tooting.
Tickets being accepted on South West Trains and London Tramlink services.
Staff at Wimbledon station have said there would be no services from platform 9 until further notice.
A spokesman from Network Rail said: "There has been an ongoing incident on the line between Tooting and Streatham today.
"Electric trains on this line collect their power from the conductor rail (also known as the third rail) through pick-ups that run along the top of it.
"A train from Sutton to Bedford suffered damage to some of its pickups and came to a stand half a mile or so from Tooting at 11.30am this morning.
"The conductor rail was also damaged in the incident and the train was unable to continue its journey
"The cause of the issue is not yet known and investigations are continuing.
"The current state of play - as of 3.15pm - is that one line remains closed between Wimbledon and Streatham.
"Engineers are on the site and repairing the damage to the track. Passengers in the area are advised to check before they travel this afternoon as services will be subject to change."
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