French rail company SNCF says 800,000 passengers have been affected by what the country’s Prime Minister Gabriel Attal described as “acts of sabotage”.
A series of fires caused the disruptions early on Friday morning, hours before the Paris Olympics opening ceremony.
Several high-speed TGV lines have been hit to the west, north and east of the capital and SNCF has warned the disruption could last for days. Eurostar has also warned customers of longer journey times and cancellations.
Nobody has claimed responsibility and Mr Attal said that security forces were searching for those responsible. The public prosecutor’s office is also investigating.
“Early this morning, acts of sabotage were carried out in a prepared and coordinated manner on SNCF installations,” Mr Attal wrote on social media.
SNF earlier described the fires as a “massive attack” involving “malicious acts”.
Transport minister Patrice Vergriete said all the information “points to the fact that these were arson attacks”.
He said the “criminal acts” happened simultaneously and “vans were found from which people had fled, particularly in the south-east”. Flammable material was found on site.
Three main routes on the TGV line connecting Paris with cities such as Lille in the north, Bordeaux in the west, and Strasbourg in the east were attacked.
The authorities said they foiled a fourth attack, to the south on the Paris-Marseille line.
Sports Minister Amélie Oudéa-Castéra described the attacks as “downright appalling”.
She added that the immediate impact on the public and Olympic athletes was currently being assessed, as well as the potential effect on transporting teams to competition sites over the weekend.
More than 300,000 spectators are expected in the heart of Paris on Friday for an opening ceremony that will see thousands of Olympic athletes sailing down the River Seine.
Paris 2024, the organiser of this year’s Olympic Games, say they are “assessing the situation” and working closely with SNCF.
The railway company’s chief-executive, Jean-Pierre Farrandou, said there was severe disruption and the impact on customers would be very significant.
Eurostar and other high-speed services have been diverted onto different lines, causing a knock-on effect to other services.
Germany’s rail operator Deutsche Bahn has warned of disruptions to its long-distance rail network and asked passengers to check their connection before travelling.
SNCF said its systems had detected acts of sabotage at about 04:00 local time (02:00 GMT).
Its teams were already on site, it added, in an attempt to investigate damage and begin repairs but warned that the situation was likely to last throughout the weekend and potentially beyond.
Mr Farrandou said thousands of rail workers were being deployed across the network.
“This was supposed to be a holiday,” he told French TV.
“It’s the big day for going on summer holiday, and it’s also of course the opening of the Olympics with lots of French people coming to Paris to enjoy the Games and all of that’s ruined.”
The attack comes as a massive security operation is in place in the French capital, involving tens of thousands of troops and police to guard against threats to the global sporting event.