Train services between Hastings and Tunbridge Wells were suspended for close to an hour while emergency services responded to reports of a trespasser near Battle, British Transport Police (BTP) confirmed.
A spokesman for BTP said officers were called to Battle station at 2.50pm.
As a result, all lines through Battle were blocked, Southeastern confirmed on Twitter.
BTP said one person was later arrested on suspicion of shoplifting and taken into custody.
He was handed over to Sussex Police, according to the BTP spokesman.
Southeastern said: “Emergency services dealt with an incident at Battle station earlier this afternoon.
“Because of this, the electric power to power our trains on this line had to be isolated, causing cancellations, delays and alterations to our trains between Tunbridge Wells and St Leonards Warrior Square. I understand that the disruption lasted around 50 minutes.”
Services are now no longer affected by this disruption, according to Southeastern.