The Paris Olympics' chief organiser Tony Estanguet said on Tuesday an opening ceremony on the river Seine was the "very probable" option, after French President Emmanuel Macron said it could be moved to a stadium.

"Today, the really main and very probable plan is to organise the ceremony on the Seine," Estanguet told RFI.

"The president was very clear yesterday. The main objective is to achieve a very beautiful, absolutely unique opening ceremony, the first time that it will be held outside a stadium, in the centre of Paris on the Seine," Estanguet said.

In an interview on Monday, Macron said France was looking forward to putting on the unprecedented ceremony in which teams will sail down the Seine, but that contingency plans were in place in the event of a security threat to the event.

He said the ceremony on July 26 could be "limited to the Trocadero" across the Seine from the Eiffel Tower and -- for the first time -- Macron said it could even be moved to the Stade de France, the national stadium.

"There are Plan Bs and Plan Cs, we are preparing them in parallel... We will analyse this in real time," Macron said.

Estanguet, who was attending the lighting of the Olympic flame in Olympia, Greece, said: "All of our energy and all of the means at our disposal are being employed to make this very beautiful ceremony a success.

"In parallel to that, we are looking at all the contingency plans to adapt to the context, because that is our responsibility.

"Depending on the situation we're in at the time, we will adapt the project."

Paris Mayor Anne Hidalgo suggested she was surprised by Macron's suggestion that the ceremony could be moved.

"The only plan I know is Plan A," Hidalgo said.

"The message I prefer to send is that we are ready and we are going to welcome the world," she added.