Chalk has fallen onto the line between Folkestone Central and Dover Priory, rendering it impassible.
Bus services are being brought in between the two stations following the landslip, which is just outside the Abbotscliffe Tunnel.
There will also only be a limited train service between Dover and Ramsgate.
While there is not a great volume of rocks on the tracks, there are fears that it is the start of a much larger fall.
Network Rail confirmed that an inspector is on the way and that the line won't be reopened until it is confirmed to be safe.
This is the third time in the space of a month that trains have been halted due to a landslip in Kent.
And this month, trains were cancelled on the line through High Brooms near Tunbridge Wells due to a landslide.
However there was a double chalkfall a couple of miles east of today's incident.
This was near Samphire Hoe, Dover, on Wednesday, February 3.
In that area the rail line was inside Shakespeare Tunnel and the chalk simply fell into the sea.
Thousands of tonnes of chalk tumbled in two collapses 10 seconds apart.
HM Coastguard afterwards warned that chalkfalls in this and other areas had been occurring because of recent wet weather.
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