Hastings line closed 'until further notice'
Network Rail has said it has no idea when the line linking East Sussex, Kent and London will fully reopen.
Train services between Hastings and London via Tunbridge Wells and Tonbridge have been disrupted since December following landslips.
The company had planned to reopen the line between Battle and Robertsbridge on 3 March.
Additional work is now needed after the repairs to the landslip near Whatlington started to move.
Engineers were working at the site to find out why the ground movement was continuing, the company said.
A spokesman said: "Whilst this detailed investigation is undertaken, the continuing ground movement around the embankment makes it difficult for Network Rail to accurately predict the work required and how soon this stretch of line can be brought safely back into use."
On Tuesday, Councillor Jeremy Birch, leader of Hastings Borough Council said the closure could have a "serious effect" on tourism in the town.
He said no-one wanting to visit the seaside town would want to travel on a bus replacement service.
The line was first affected by a series of landslips in December.
More than 10,000 tonnes of stone were used for the repairs at Stonegate on the line between Hastings and Tunbridge Wells.
Southeastern first announced the line would fully reopen on 3 March, but with a reduced timetable.
However, more rain caused further landslides around Whatlington, which meant buses had to continue to replace trains between Battle and Robertsbridge.
The Network Rail spokesman said: "Rail replacement bus services will continue to operate between these stations until further notice."