PARIS, Dec 13 (Reuters) - Paris 2024 organisers are expecting at least 600,000 to attend the Summer Olympics opening ceremony on the Seine as athletes and delegations will sail along the river to kick off the Games. Some 160 boats will set off on July 26 from the Pont d"Austerlitz for a six-kilometre journey to the Pont d"Iena in an event Tony Estanguet, the head of the organising committee, described as "unique and spectacular". "We"ve been working on it for the past 12 months, it"s the result of a collective effort with the IOC (International Olympic Committee) and all authorities. It has to be spectacular," Estanguet told Reuters in an interview. "It will be the first time people have free access to the opening ceremony, and not just in a stadium. It will also be a popular event." While the lower part of the river bank will be subject to ticketing, there will be free access to the upper part with spectators able to see holograms on the water, dancers on the roofs of nearby buildings and aerial shows. Some 80 giant screens will also be installed along the route. "The Games is a unique, once-in-a lifetime experience. We want people to feel it. (The boats) will pass along the iconic landmarks of Paris - Notre Dame, the Orsay and Louvre museums, the Pont Neuf (Paris"s oldest bridge), the Pont Alexandre III, the Grand Palais, the Eiffel Tower," Estanguet added. He did not say where the Olympic flame would be lit. "Let"s reconvene next year for that," Estanguet told a news conference on Monday, adding that the cost of the four ceremonies (Olympics and Paralympics opening and closing ceremonies) would be assessed in 2022. Sports minister Roxana Maracineanu added: "Let"s keep in mind that less than 5% of the facilities need to be built for this Games." RIVER PARADE Estanguet, a three-time canoeing Olympic champion who took part in four Summer Games, said the athletes would lead the river parade. "I participated in the ceremony between Sydney (2000) and London (2012). Athletes get into the stadium in the second part, after the show," he explained. "We wanted this ceremony to start with the athletes parade. It"s a fantastic way to connect the people to the athletes. It"s also better for them to sit on a boat than stand in a stadium for hours." The project was approved by the IOC last month, with its President Thomas Bach saying all security requirements would be met. Paris has been on high alert since a series of jihadist-inspired attacks in which 130 were killed and hundreds injured on Nov. 13, 2015. "Security has been our top priority since the very beginning," said Estanguet. "Public authorities have been working on it and over 50 meetings have been organised to set all the possibilities, how we can share responsibilities with the national and local forces and the private sector in terms of security."