The parade on Friday evening will see up to 7,500 competitors travel down a six-kilometre (four-mile) stretch of the Seine on a flotilla of 85 boats.
But early Friday, French rail operator SNCF said the country's high-speed network had been targeted by "malicious acts" aimed at paralysing the system.
Transport Minister Patrice Vergriete said it was an "outrageous criminal act" and Sports Minister Amelie Oudea-Castera described the attacks as "downright appalling".
French security forces have warned for months of the danger of attacks aimed at destabilising the Games.
Suspicion will fall on Russia, whose team is banned from Paris in response to the Kremlin's invasion of Ukraine. France is seen as a particular target due to its support for Kyiv.
However, far-left groups within France have a history of targeting the rail network with arson attacks.
Compared to the Covid-blighted 2020 Tokyo Olympics, which were delayed by a year and opened in an empty stadium, the Paris opening ceremony will take place in front of 300,000 spectators and an audience of VIPs and celebrities from around the world.
Rain threatened to blight the ceremony after forecasters said there was a 70-80 percent chance of rain during the ceremony.
President Emmanuel Macron told a pre-Games dinner for heads of state and government: "Tomorrow you will have one of the most incredible opening ceremonies."
The line-up of performers is a closely guarded secret but US pop star Lady Gaga and French-Malian singer Aya Nakamura -- the most listened-to French-speaking singer in the world -- are rumoured to be among them.
It will be the first time a Summer Olympics has opened outside the main athletics stadium, a decision fraught with danger at a time when France is on its highest alert for terrorism.
For months, organisers have been dogged by questions about whether they would need to scale back or move the procession, but they had insisted throughout that there was no Plan B.
Paris Braces for Olympics Opening as Rail Network Is Sabotaged
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