Passengers travelling in and out of London are facing delays after rail and Underground services were cancelled or delayed.
Some South West Trains to and from Waterloo station were cancelled or diverted because of an electrical supply problem to the level crossings between Barnes and Richmond in south-west London.
Alerts on the company's website advised passengers of the changes resulting from the disruption.
These included: no trains running between Barnes and Twickenham in south west London; the London Waterloo circular service departing at 07, 15, 37 and 45 minutes past the hour was cancelled; and the service that runs between London Waterloo and Reading is diverted, and would not call at Richmond or Twickenham.
A spokesman for the South West Trains-Network Rail Alliance said the maximum delay passengers would face was just over 20 minutes.
He said: "We would like to apologise to our customers for the disruption to their services. Engineers are working hard to resolve the problem so we can return services to normal as soon as possible. Passengers may use London Buses and London Underground on any reasonable route."
But passengers were also affected by a number of planned closures on the Tube network, including the Bakerloo, Circle, District, Hammersmith and City, Metropolitan, Northern and Victoria lines.
A spokesman for Transport for London said: "After a pause in major upgrade work in the lead-up to, and during, the Olympic and Paralympic Games, the work to replace old track, signals and trains restarted in mid-September.
"This work will further improve performance and deliver reliable Tube services for Londoners - with faster and more frequent journeys, fewer delays and, ultimately, 30% more service across the network.
"Every effort is being made to keep disruption to an absolute minimum and, through detailed planning, the effect of the works has been reduced by 10% compared to last year and by 25% compared to two years ago."