Eurostar services have been suspended following a fatality on the line in Kent.
British Transport Police (BTP) and Kent Police were called to the incident at about 11:40am on the line close to Crismill Lane in Bearsted after a person was hit by a train.
Eurostar has advised passengers who were due to travel today to exchange or refund their tickets and try to complete their journey on another day.
It said in a statement: "Due to a person hit by a train between Ashford International and Ebbsfleet International, the High Speed line is currently closed.
"As a result Eurostar trains are subject to delay and cancellation this afternoon. Emergency services are attending the incident and as soon as they advise the line can reopen our service will resume – we expect to update further soon."
In a statement, the BTP said the incident was being treated as "non-suspicious", adding: "Officers are currently working to establish the identity of the person and how they came to be on the tracks".