A railway line that suffered "significant damage" after a landslip during heavy rainfall is to remain closed "for the foreseeable future".
The track between Tonbridge, in Kent, and Redhill, in Surrey, has been closed in both directions since 22 December after the River Eden burst its banks.
Fiona Taylor, of Network Rail, said there had been "a significant earthworks failure" near Godstone.
Engineers said it could not be fixed until the ground stopped moving.
Ms Taylor said it was "a huge challenge in a very remote location".
"At the moment we have technical engineers on site ascertaining what we can do to fix the problem."
Network Rail said it was difficult to say how long it would take to repair.
It tweeted: "At the moment we are faced with either approaching the site from the north, which would require us to build a road, cut through an old embankment and bridge a river; or the south, which would require removing a slice of the whole embankment."
Southern rail said it was working closely with Network Rail and waiting to receive an estimate of when the line could reopen.
Until 5 January, buses are replacing trains between Redhill and Tonbridge, and a minibus will also be in operation between Nutfield station and Redhill.
From Monday 6 January, a shuttle train service will operate in both directions between Tonbridge and Edenbridge, which will then connect to a bus service between Edenbridge and Redhill.