Southeastern Railway say trains are currently delayed between Gravesend and Dartford.
Trains on the Swanscombe line have been delayed after reports of a trespasser on the tracks.
Police are on site working to apprehend the person, but trains between Dartford and Gravesend will be delayed in the meantime.
Reports of a trespasser on the railway near Swanscombe emerged at around 9:30am.
Southeastern said: "A trespasser has been reported on the railway near Swanscombe.
"Response staff and emergency services are on site, but trains may be delayed between Dartford & Gravesend while they work to apprehend the person."
Fastrack buses between Dartford and Gravesend are available to passengers for no extra cost, the line is expected to return to normal service at around midday.
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