PARIS — As the countdown clock to the Paris Olympics passed the 100-day mark, questions over holding the opening ceremony on the Seine River loomed large over the milestone celebrations on Wednesday.

Organizers have planned a parade of about 10,500 athletes through the heart of the French capital on boats down a 6-kilometer (3.7-mile) route along the Seine during the opening ceremony at sunset on July 26.

But, French President Emmanuel Macron said on Monday that the exceptional open-air event in central Paris could be shifted to a more conventional opening ceremony at the Stade de France if the security threat is deemed too high.

"If we think there are risks, depending on our analysis and the context, we have fallback scenarios. There is a plan B and a plan C," Macron said.

France is on high security alert ahead of the Paris Olympics and Paralympics, which are expected to draw millions of visitors to the country. Organizers, French government officials and French athletes at the J-100 ("100 Days To Go" Olympic event) on Wednesday all acknowledged security concerns over the opening ceremony, which will bring huge crowds, and over 100 world leaders, to the river's embankments.

They insisted that preparations for the parade on the Seine are still in full swing and are set to go ahead as planned.

"We are working heavily on Plan A, which remains the central scenario, and the very, very dominant scenario," France's Sports Minister Amelie Oudea-Castera said.

She added, enthusiastically and with a large smile: "We keep working on that fantastic ceremony on the River Seine."

The sports minister emphasized that visitors to Paris will be safe during the Olympics.

"We know that risks exist," Oudea-Castera said. "We know the world is complex, sometimes unstable, sometimes unpredictable, sometimes dangerous," she said, before insisting: "We really want to say to the whole world that, in any case, France will be a safe place."

Tony Estanguet, the head of the Paris Games' organizing committee, said the plan to open the Games with the sunset parade on the Seine remains unchanged, adding "it's our duty, our role, to make sure it will happen".

However, there are, as yet unspecified, contingency plans in place, whereby organizers will adapt to any circumstances that might arise, Estanguet added.

David Lappartient, president of the French National Olympic and Sports Committee, accepted there are challenges in preparing an event like the Olympics in a city like Paris at a time of heightened global tensions.

"The situation worldwide is quite complicated," said Lappartient, who is also an International Olympic Committee member. There are challenges with transport and security, and it's reasonable and reassuring that the "government is trying to see all the options on the table."

Former France handball star Michael Guigou, who won multiple Olympic and world titles, said security risks have become part of daily life in France, such as when he goes to a concert, but added that he has full trust in security arrangements at the opening ceremony — wherever it may take place — and in fan zones, Olympic venues and the city of Paris itself.

"It's part of life today, unfortunately," Guigou said. "We have enough intelligent and competent people in place to look after that, so I'm not doubting things."

Dany Dann, a French breaker who will take part in his first Games when breaking makes its Olympic debut in Paris, has no concerns.

He is only anxious to get started, on the Seine, at the Stade de France — or anywhere else in Paris.

"I just want to live the Games," Dann said. "We know that if it's moved left or right, things will be organized so that everything's fine. I am just concentrating on my own preparations."

Agencies via Xinhua