French President Emmanuel Macron declared the Olympic Games open on Friday after a soaking wet ceremony in which athletes were cheered by the crowd along the Seine as dancers took to the roofs of Paris.

France's three-time Olympic gold medallists Marie-Jose Perec and Teddy Riner then lit the Olympic cauldron, suspended on a hot-air balloon, before Canada's Celine Dion sang Edith Piaf's "Hymn to Love", in her first public performance in years, drawing huge cheers from the crowd.

A fleet of barges took the competitors on a 6 km-stretch of the river alongside some of the French capital's most famous landmarks, as performers recreated some of the sports to be showcased in the Games on floating platforms.

It was the first time that an opening ceremony has taken place outside a stadium, adding to the headaches for a vast security operation.

"I invite everybody: dream with us. Like the Olympic athletes, be inspired with the joy that only sport can give us. Let us celebrate this Olympic spirit of living in peace," International Olympics Committee President Thomas Bach said as the ceremony came to an end at the foot of the Eiffel Tower.

A mix of French and international stars, including soccer great Zinedine Zidane, 14-times French Open champion Rafa Nadal, 23-times Grand Slam champion Serena Williams and three paralympic athletes were among the last torchbearers before the cauldron was lit.

It will blaze until the closing ceremony on August 11.

While rain forced some fans to leave early, those who spoke to RTHK's Hailey Yip and Kelly Yu were impressed by what they saw.

"I thought it was very beautiful," one French spectator said. "Very artistic, very creative, very French, lots of contrast, lots of great pictures, so I think it was fabulous."

Earlier, crowds cheered as the teams headed down the Seine on a series of barges. The Hong Kong, China team deployed umbrellas as heavy rain struck, with athletes including flag-bearers Siobhan Haughey and Edgar Cheung snapping selfies along the way.

Team China, led by table tennis star Ma Long and synchronised swimmer Feng Yu, represented one of the biggest national delegations. (Reuters/RTHK)