All Eurostar trains between London and Paris have been cancelled after an unexploded Second World War bomb was found near train tracks.
Thousands of passengers are facing disruption as the cross-Channel operator halted 10 services on Friday morning.
All trains from Paris to London are suspended until at least after midday and pictures from Gare du Nord show large queues of people.
Eurostar said in a statement: “Due to an object on the tracks near Paris Gare du Nord, we are expecting disruption to our services this morning.
“Please change your journey for a different date of travel.”
France’s national train operator SNCF said services at Gare du Nord would be suspended until mid-morning at the request of the police.
“We invite travellers to postpone their trip,” it said in a statement.
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Trains to northern France have also been brought to a halt from Gare du Nord, which is a major European transport hub.
First and Second World War bombs are regularly discovered around France but very rarely in such a densely populated area.
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