Services travelling from the coast, Horsham or Gatwick Airport towards central London may be delayed or revised to call at different stations, Southern Rail said on Twitter.
Southern, Gatwick Express and Thameslink services are affected.
In a statement, the rail operator said: “Please listen carefully to onboard announcements and check the departure boards before you join your train.
Services running through Earlswood may be delayed or revised.”
Southern, Gatwick Express and Thameslink tickets are being accepted across all three operators via Gatwick Airport, Southern added.
Metrobuses are in place between Gatwick Airport, Horley, Salfords, Earlswood, Redhill and Merstham.
Ticket acceptance is also running on TfL Buses between Redhill, Dorking and central London (including route 405 to/from Redhill), on South Western between the South Coast, Clapham Junction and London Waterloo and on trams across the Croydon area.
A spokesman added: “Trains are unable to run via Redhill.
“Additionally, some Thameslink and Gatwick Express services which start or finish their journeys at Gatwick Airport may be cancelled.
“This will help prevent congestion in the area.”