Trains in France face disruption until Monday after a “massive attack” hit the network ahead of the start of the Paris Olympic Games.
A series of fires are reported to have affected high-speed rail lines across the country.
Some Eurostar services to and from the French capital are being cancelled, with delays to Channel Tunnel services from London.
An estimated 800,000 passengers are affected across the SNCF French rail network.
The Foreign Office warned in a travel alert for France this morning: “There are reports of disruption across main line train services affecting Eurostar services and domestic high speed trains in several parts of France.
“French railways state that services could be disrupted until Monday 29 July and are advising travellers to postpone travel if possible.
“Check with your travel operator, or railway operator’s website.”
SNCF said: “Last night, the SNCF was victim of several acts of vandalism on the Atlantic, Northern and Eastern high-speed lines. Fires were deliberately set to damage our installations.”
Eurostar said: “Due to co-ordinated acts of vandalism in France, affecting the high speed line between Paris and Lille, all high speed trains going to and coming from Paris are being diverted today.
“This extends the journey time by around an hour and a half. Several trains have been cancelled.
“Eurostar’s teams are fully mobilised in stations, in the call centres, and onboard to assist and ensure our passengers are fully informed. Customers are being informed via email, SMS and on Eurostar.com.”