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A police helicopter is understood to have been scrambled to assist a search for a trespasser on the tracks who has caused trains to be cancelled.
Power to the lines was switched off at about 7.30pm following the incident near Margate station.
Trains cannot run between Herne Bay and Ramsgate or between Ramsgate and Canterbury West, according to Southeastern.
A replacement bus is running between Ramsgate and Herne Bay.
Southeastern said at 8.30pm that the power was set to be switched back on once emergency services were clear of the line.
But 20 minutes later, it tweeted: "Unfortunately the power has had to be switched off again in the Margate area as emergency services need to return to the track to deal with the incident."
At 9.12pm, Southeastern said: "The power has been switched back on at Margate now, and trains are running through the area again. Trains may still be delayed through the area following the trespasser on the line earlier."
A police helicopter is assisting the search, according to residents.
Kent Police and British Transport Police have been approached for comment.