Commuters from Brighton, Hove and Portslade were being warned to expect a second day of rail chaos.
The warning comes as workmen try to clear the debris from a landslip yesterday (Monday 1 August) and carry out emergency repairs.
The landslip, in the South Croydon area, was caused by a burst water main which was reported at about 9.30am yesterday.
All five lines of track between East Croydon and South Croydon were impassable and it took until about 7pm before two lines could be reopened.
Thousands of commuters queued in the blazing heat for replacement buses as the rush hour got under way.
Despite repair and maintenance crews working through the night, Southern and First Capital Connect warned of further disruption today.
Southern said that services would be running as normal from Brighton, Hove and Portslade to London, except as listed.
The Brighton to London Victoria services at 6.30am, 6.56am and 7.30am will not run.
But the Gatwick Express services at 6.40am, 7.15am and 7.44am from Brighton to Victoria will also call at East Croydon and Clapham Junction.
The same operator’s trains on the hour and at half past the hour will also stop at East Croydon and Clapham Junction on their way back to Brighton.
The 8.13am Brighton to Victoria service, though, will start from Gatwick at 8.50am.
Southern said that the Victoria to Brighton trains at 8.51am and at the same time every hour until and including 3.51pm will not run.
And the Brighton to Victoria services from 9.25am to 2.25pm inclusive would also not run.
South Croydon and Purley Oaks stations will be closed all day.
Network Rail said that customers were advised to use local bus services between East Croydon and Purley.