Commuters have been plunged into travel chaos after a four metre-deep hole was found under a railway track.
Southern and Thameslink passengers have been warned to avoid the key transport link at London Bridge after the hole was found at Forest Hill, south east London.
Network Rail said it is moving more than 50 tonnes of ballast to the scene to try and shore up the track, but warned that travel problems may last to the end of the day.
The hole has shut down two lines into London Bridge and has severely disrupted, diverted or cancelled many Southern services into and out of station.
The rail operator said the London bound lines are "blocked" due to the large hole affecting the track between London Bridge and East Croydon.
Passengers have been told to use either Victoria or Blackfriars. Southern tickets are being accepted on London Buses, London Underground, South West Trains, Southeastern and London Overground services on any reasonable route.
In a statement, Network Rail said: