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The high speed line has reopened after a person was spotted near the tracks earlier this evening.
Eurostar services have were also stopped and passengers at St Pancras reported they were initially held in the London station.
British Transport Police were called at about 8pm.
Passengers around Kent were left waiting on cold platforms and expressed their frustrations on social media.
Some report delays of several hours on both the Southeasternhih speed service and Eurostar.
The high speed services were not able to run for more than three hours.
It is thought the trespass incident has been resolved and British Transport Police have been contacted for comment.