A Waterloo and City Line train has derailed.
The front two wheels of the train “slipped off the tracks” as it came out of the depot near Waterloo Station.
Only the driver – who was not injured – was onboard the train, Transport for London said.
The train derailed at 6.30am, with it now blocking the line.
Commuters who use the line – which runs from Waterloo to Bank – are being advised to find alternative routes.
He added the line would be reopened “as quickly as possible”.