Eurostar has suspended services between London and Paris for the rest of Friday after the discovery of an unexploded Second World War bomb near tracks in the French capital.
Thousands of passengers are disrupted as the cross-Channel operator was scheduled to run 32 trains in either direction throughout the day.
A large crowd of people who were booked on affected services has gathered outside the check-in area at London St Pancras station.
Eurostar said in a statement: “Due to the discovery last night of an unexploded bomb from the Second World War during work carried out on the tracks in St Denis (north of Paris), traffic has been completely halted to and from Gare du Nord.
“As a result, all Eurostar trains are cancelled to and from Paris today.”
Lauren Romeo-Smith, part of a group at London St Pancras who were planning to visit Paris for a birthday celebration, told the PA news agency: “We would have thought there would be more Eurostar staff.
“We’re looking up flights, but our options are limited.”
Charlotte Kidd, who was scheduled to visit Disneyland Paris to celebrate her 30th birthday this weekend, said she is still hopeful of getting there.
She said: “We’ve got two hours. If not, we’ll try and get there some other way.”
Emma Roe, part of a group of eight friends, said they have considered booking flights from Luton Airport to Amsterdam but there is nothing available until 6pm.
She added: “We’re all parents, so we don’t want to lose our free weekend.”
Eurostar is giving passengers whose trains have been cancelled the option of either requesting a refund or voucher for the value of their booking, or to re-book for travel on an alternative service.
Five of the six flights that British Airways is operating from Heathrow to Paris Charles de Gaulle on Friday after midday are full.
Ticket for the one with spare seats, which departs at 8.30pm, are being sold for £357.
All three of easyJet’s flights from Gatwick to Charles de Gaulle on Friday after midday are fully booked.
French transport minister Philippe Tabarot told broadcaster Sud Radio that trains using Gare du Nord will be “strongly disrupted” throughout the day, with only a limited service resuming in the afternoon.
Fridays are one of the busiest days of the week for Eurostar, as many leisure travellers embark on international weekend breaks.
The bomb was discovered at around 4am.
A spokesperson for Eurostar said it was found during work on tracks in the St Denis area, north of central Paris.
This resulted in the suspension of all services to and from Gare du Nord, which is Eurostar’s station in Paris.
Services will only be permitted to resume once “mine clearance operations” by the French police are completed, the spokesperson added.
Bombs left over from the First and Second World Wars are regularly discovered in France, but it is rare for them to be found in such densely-populated areas.
Gare du Nord also connects Paris with other international destinations such as in Belgium, the Netherlands and Germany, as well as being used for domestic services.
It is considered the world’s busiest railway station outside of Japan.
Trains between London and Brussels are unaffected.
Press Association