Israel's footballers take on Mali in the men's competition, under the watchful eye of 1,000 police officers, with authorities erecting an "anti-terrorist perimeter" and bracing for possible disruption around the stadium.
A French police source told AFP it was possible that "people shout insults from the stands" or that there is "whistling and flags shown during the hymns, for example."
Israel's participation in Paris has been a key talking point in the run-up, with calls from the Palestinian Olympic Committee and some left-wing French MPs for the country to be excluded over the Gaza war.
President Emmanuel Macron stressed the Israeli athletes were "welcome in our country", adding it was "France's responsibility to provide them with security."
Meanwhile, a packed Stade de France will cheer on Antoine Dupont -- arguably the world's best rugby player and a pin-up of the Paris Games -- as the Rugby Sevens tournament starts.
The electric Dupont is the biggest draw for the 555,000 fans expected over the six days of rugby action, but France will have their work cut out to stop double Olympic champions Fiji.
France and Fiji are in the same pool and will play the United States and Uruguay, before the pair face each other in a mouthwatering clash on Thursday.
Others to watch in the wide-open competition are traditional rugby powers New Zealand, Australia, Argentina, and Ireland.
'There's no one'
Preparations for Friday's historic opening ceremony were in full swing with an unprecedented security operation for the athlete's parade along the River Seine.
Around 6,000-7,000 athletes are set to sail down a six-kilometre (four-mile) stretch of the river towards the Eiffel Tower, on 85 barges and boats.
Up to 500,000 people are set to watch in person from specially built stands, on the river banks and from the overlooking balconies and apartments.
The area around the river has been locked down before the ceremony, with snipers positioned along the route and frogmen deployed to prevent a waterborne attack.
The entertainment line-up for the ceremony, the first time a Summer Olympics has opened outside the main stadium, is yet to be fully announced.
But videos posted online showing US pop star Lady Gaga in Paris sparked rumours she will be among the performers.
American rapper Snoop Dogg will carry the Olympic flame this Friday as it makes its final rounds before the ceremony.
Some Paris business owners grumbled the security measures were hurting their bottom line.
"We were told there would be loads of people during the Olympics and even before. But in fact, no. There's no one," Jonas Seignovert, manager of the Eugene restaurant, told AFP.
In the first scandal of the Games, a video emerged showing the mistreatment of a horse that led to one of Britain's most decorated Olympians, dressage specialist Charlotte Dujardin, being ejected from the Paris Games.
The video showed three-time Olympic champion Dujardin walking alongside a horse and repeatedly whipping the animal while training a young rider.
Dujardin, 39, who has won six Olympic medals and was aiming to become Britain's most successful female Olympian by winning further medals in Paris, has admitted to an "error of judgement" and said she was "deeply ashamed" of her actions.
Financial guarantees'
With one Games about to start, France is already looking to host another Olympics, as the International Olympic Committee awarded the 2030 Winter Games to the French Alps.
The IOC handed the games to France but under the condition that Paris stumps up the required financial commitments.
France is the only candidate to host the 2030 Games but the funding has been in question because there is no government in place following inconclusive snap elections.
Macron told IOC members he would ask France's next prime minister to give a financial "guarantee" for hosting the Games.
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