French rail officials warned of travel chaos for hundreds of thousands of people throughout the weekend after saboteurs following a meticulous plan paralysed much of the train network on Friday as the Olympic Games started.

No immediate claim of responsibility was made for the arson attacks on cabling boxes at junctions strategically picked out north, southwest and east of the capital where the Olympics opening ceremony was staged on Friday night. Rail workers thwarted a fourth attempt to destroy safety equipment.

The SNCF rail company called it a "massive attack".

"Our intelligence services and law enforcement are mobilised to find and punish the perpetrators of these criminal acts," Prime Minister Gabriel Attal posted on X, calling the attacks "prepared and coordinated acts of sabotage".

Services from Paris to much of France saw mass cancellations and delays.

The Eurostar company said it scrapped about a quarter of its trains between London, Paris, Brussels and Amsterdam. It predicted cancelling about a fifth of trains over the weekend and all services will face delays.

British Prime Minister Keir Starmer had to take a plane instead of a high speed train to the Olympics ceremony. Four special trains bringing Olympic athletes to Paris, including some US team members, went ahead, SNCF said.

With one of France's busiest holiday travel weekends clashing with the start of the Olympics, SNCF said about a quarter of trains will be cancelled on Saturday and Sunday on the lines attacked. Trains that run will face delays.

The company said thousands of staff worked to repair the damage and try to get services running again. It estimated that about 250,000 passengers were affected on Friday. Junior transport minister Patrice Vergriete said 800,000 could face the fallout over the three days.

At each site, the perpetrators targeted fibre optic cables that carry safety information for drivers and control rail changes, SNCF chief executive Jean-Pierre Farandou said.

Gerard Due, mayor of Croisilles in northern France, one of the sites hit, said the attackers had specialised equipment to access the cables and then "threw a flammable liquid" on them.

Vergriete said that the saboteurs had been spotted with "vans", while "incendiary devices were found at the scene".

French security forces are on their highest alert to prevent attacks during the Paris Olympics. (AFP)