Trains have started running again between East Croydon and Gatwick after all services in the area were cancelled earlier for much of the day.
Southern is running two trains an hour from Victoria to Brighton – starting at 7pm – after the main line was closed by a landslip in the South Croydon area.
The landslip was caused by a burst water main in Stanhope Road, Croydon, which was reported at about 9.30am.
Southern said that trains would leave Victoria at 7pm, 7.30pm, 8pm, 8.30pm, 9pm and 9.30pm.
The trains will call at Clapham Junction, East Croydon, Gatwick, Three Bridges, Haywards Heath and Brighton, taking an hour and five minutes to reach Brighton.
Victoria to Littlehampton trains via Hove and Portslade are scheduled to leave London at 7.17pm, 8.17pm, 9.17pm, 10.17pm and 11.17pm.
They are scheduled to take just over an hour, arriving in Hove at 24 minutes past the following hour, and at 28 minutes past in Portslade.
Some routine services are running from Brighton to Victoria and from Portslade and Hove.
A shuttle train service is operating in both directions between the Brighton and Redhill, Littlehampton and Gatwick, via Hove and Portslade, London Bridge and East Croydon, and London Victoria and East Croydon.
Thousands of rush-hour commuters had to queue to use replacement buses between East Croydon and Redhill earlier.
The line was covered in debris and water after the landslip this morning.
And as services were halted many railway staff were unable to use the trains to get to where they were needed.
First Capital Connect, which runs Thameslink services between Brighton and London Bridge, Blackfriars and King’s Cross, said: “It is hoped that two of the five lines will reopen at approximately 18.30 and that the first train from London Bridge will be the 19.12 service to Brighton calling at East Croydon, Gatwick Airport then all stations to Brighton.
“We strongly advise customers to travel before 22.00 as it is likely that further repair work to restore the remaining lines will take place after this time.
“A reduced and revised service will also be in place on Tuesday 2 August.
“Full details will be available on our live train updates page as soon as they have been confirmed.
“Please check before travelling.”
Many drivers on the M23 also suffered some delays. It is believed that holidaymakers heading for Gatwick who might have taken the train followed advice and drove instead.