Paris (AFP) - The opening ceremony for the Paris Olympics began Friday, an unprecedented and ambitious show with up to 7,000 athletes parading down the River Seine past the historic monuments of the French capital despite the risk of rain dampening spirits.

For the first time in Olympic history, the opening ceremony is taking place outside the main stadium, with some 300,000 people watching in person from specially built stands on the river banks, and another 200,000 from overlooking balconies and apartments.

As tradition dictates, the Greek delegation had the honour of leading out the flotilla, as the cradle of the modern Olympic movement.

In an ambitious, high-risk departure from past opening ceremonies, the athletes will sail down the river in an armada of 85 boats.

The show will blend both French culture and history and great Olympic moments of the past while US pop star Lady Gaga wowed the crowd of VIPS and spectators with an early performance in the ceremony.

Despite the forecast of heavy rain, and a wave of attacks which paralysed France’s high-speed rail network early Friday, organisers were confident of pulling off the audacious ceremony.

Chief Games organiser Tony Estanguet said before the show there would be some modifications if it was wet, but he insisted the weather would not dampen the mood.

“It’s going to be a beautiful moment, it’s going to be a great party,” he added.

Basketball superstar LeBron James, who will be one of two Team USA flagbearers along with tennis star Coco Gauff, was seen being equipped with a clear plastic poncho to protect him from the predicted deluge just before the teams boarded the boats.

- Long queues -

Long queues had formed at access points along the Seine hours before the start of the parade.

After passing scanners and checkpoints, the first arrivals discovered the numerous floating stages installed in the river channel and bridges that have been festooned with flags and the pink-and-purple colours of the Games.

“The atmosphere is really friendly,” said 75-year-old Frenchman Jean-Yves Herve, who watched the show with his grand-daughter.

“There are lots of foreigners, we’re enjoying it. It’s good for France.”

A huge security operation was in place for the ceremony, with a security perimeter erected along both banks of the Seine.

The ceremony will be guarded by 45,000 police and paramilitary officers and another 10,000 soldiers and 22,000 private security guards will complete the security operation.

Police snipers were positioned on high points along the river, which is overlooked by hundreds of buildings.

- Hunt for culprits -

French security forces are on their highest alert to prevent terror attacks spoiling the start of the first Olympics in Paris in 100 years, while acts of sabotage from hostile foreign powers were also a known risk.

French officials refused to comment on the identity of those responsible for the rail sabotage who appear to have had a sophisticated understanding of the network.

Far-left French anarchists have a history of targeting the train network with arson attacks.

Suspicions might also fall on Russia, which French President Emmanuel Macron has said in the past was planning to target the Games.

Around 3,000 dancers are set to perform from the banks of the river and monuments including Notre-Dame cathedral in a show that will promote diversity, gender equality and French history.

The landmarks and architecture of the City of Light are set to feature as a backdrop both to Friday night’s show and much of the sport afterwards.

Paris’s vision is for a more cost-effective and less polluting Olympics than previous editions, with competitions set to take place at historic locations around the capital.