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Trains between Folkestone and Dover are delayed after chalk rocks fell onto the line.
A host of services across east Kent have been disrupted and there are currently hold-ups of 30 minutes.
Engineers arrived on site in Dover to carry out urgent safety checks, with services between Ashford and Folkestone being heavily affected as a result.
Rocks had fallen from the high embankment and tumbled down onto the tracks.
The line between Dover and Folkestone was shut in both directions, and replacement buses are still running between Dover and Ramsgate.
Southeastern says that despite the reopening of the line, services are still held-up and some diverted.
There is now a safety speed restriction in place through the affected area.
The train operator hopes to have services back to normal soon.