TWITTER•GETTY The hole is six foot wide and up to 50 feet deep

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Southern and Thameslink passengers were warned to avoid the key transport link at London Bridge with many services cancelled or diverted. The hole was found at Forest Hill in south-east London on Monday afternoon. Thames Water confirmed that a sewer under the track had collapsed and described the repair operation as "extremely complex". The appearance of the hole, which was classified by Network Rail as a "hole" rather than a "sinkhole", further delayed trains for the operator which has been plagued by problems for several months.

GETTY Southern Rail said the hole appeared at 1pm

Network Rail (NR) closed all four lines between East Croydon and London Bridge. Mainline trains to London Bridge from Littlehampton, Bognor Regis and Eastbourne were cancelled and the disruption was expected to continue throughout Tuesday. Paul Rutter, area director for Network Rail, said: "Following investigations, a collapsed sewer has been found at the site of the hole which was found on the railway in the Forest Hill area yesterday. "Network Rail engineers have been working with our counterparts at Thames Water throughout the night to identify and fix this problem as quickly and as safely as possible.

TWITTER Southern insisted the incident was caused by a "hole" rather than a sinkhole

"Because of the location of the hole we are unable to run trains on this track through to London Bridge this morning and it looks likely that disruption to services will continue throughout the day. "Passengers are advised to check before they travel and allow extra time for their journeys. Further details will follow as soon as they are available. "We apologise sincerely for the disruption and assure passengers both Network Rail and Thames Water are working hard to restore the railway to full capacity." Danny Leamon, Thames Water's senior operations manager, said: "We're acutely aware of the importance of this rail route. Our specialist teams worked through the night, and they'll continue to work as fast as possible today to get the pipe fixed and help Network Rail get the track reopened. "Our sewer is below the track, but it is too early to say whether the sewer pipe is the cause of the sinkhole. "This is an extremely complex job as the pipe is in a difficult location in the tracks and six metres below the ground. Engineers hope to finish repairs later today but we're unable to put an exact time to it at this stage."