Eurostar has cancelled all services to and from London until further notice after strike action hit the cross-Channel route.
A “last-minute strike” at the Channel Tunnel operator, Eurotunnel, has also hit LeShuttle services on the route.
The disruption emerged as many people start travelling for the Christmas holidays over the next few days.
Eurotunnel said it did not know how long the action would last, but was working to end it as soon as possible.
Separately, there are no trains from London Euston station on Thursday because of damaged overhead power cables between Milton Keynes and Watford Junction.
As a result, Euston station is currently closed to incoming passengers. Network Rail engineers are currently assessing the damage to the cables using drones.
Services through the Channel Tunnel are suspended after a range of Eurotunnel staff – from those who run the trains to those who manage and maintain the infrastructure – walked out at short notice.
Eurostar, which runs high-speed passenger trains on the route, said: “Customers affected will receive direct communication about their journey and can exchange their tickets free of charge or claim a refund.
“We are closely monitoring the situation as it evolves, and any further updates will be communicated as soon as possible.”
Several thousand people were also due to use the Le Shuttle service run by Eurotunnel, which carries cars through the tunnel on trains.
Eurotunnel said it was putting people on ferries while services are suspended, due to an arrangement with ferry companies.
Unions called the strike at 11:00 GMT. Under French union law they can run the strike for as long as they like, and there is no indication at the moment how long it will go on for.
Staff were offered discretionary bonus of a €1,000 (£867) bonus, but the unions’ request is for three times that much.
Eurotunnel said it was working to bring the strike to an end as soon as possible, and had been in contact with the unions on Thursday afternoon.