A “do not travel” alert has been issued by three train operators on Wednesday morning.
Train operators Southern, Thameslink and Gatwick Express said passengers should not to travel “if at all possible” because of “multiple incidents”.
Issues include a train derailment inside a depot in Selhurst, south-east London, and a fault with the signalling system between London Blackfriars and Norwood Junction.
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Southern told passengers: “If you are travelling on our network today, your journey may be delayed and you may need to use an alternative route to reach your destination.
“If you can, please delay your journey until later today.
“Please check your train before travelling and allow an additional 60 minutes for your journey.”
National Rail Enquiries said the signalling fault means fewer rail lines are available between Norwood Junction and London Blackfriars, and trains running on the available lines must travel at slower speeds than normal.
That means services are suspended on routes between: London Bridge and East Grinstead; Orpington and Luton; Brighton and Cambridge; and Bedford and Three Bridges.
Trains that usually run between Welwyn Garden City and Sevenoaks are only operating between London Blackfriars and Sevenoaks.
Services between Rainham and Luton are only running between Rainham and Dartford.
Trains that normally operate between Horsham and Peterborough, or Brighton and Bedford, may run via Selhurst instead of Norwood Junction.
