A broken down train at Balham has led to the cancellation of some routes in south London and disruption on the Southern railway network, while flooding has also caused some problems on Thameslink services.
The broken down train incident was reported at 6.46am and has affected services between Balham and London Victoria, with delays of up to 30 minutes.
Some services, such as Epsom Downs to London Victoria, would no longer stop at Wandsworth Common and Battersea Park during the disruption, Southern said.
Delays have also been reported on services between Clapham Junction and West Croydon.
First Capital Connect Thameslink services have also been delayed, with station announcements saying there have been problems with flooding.
Commuters on the Wimbledon loop to Sutton have been delayed and at least one train has been cancelled.