Hundreds of thousands of people lined the Avenue des Champs-Élysées in ⁠Paris on Saturday to attend an open-air mass with Pope Leo, on the second day of his visit to France.

The Vatican estimated 700,000 people turned out for the outdoor mass with the 71-year-old American pope – about 100,000 more than the number of people who had registered to attend.

It took place at the Place de la Concorde, the site of bloody executions by guillotine during the French Revolution – when Louis XVI’s staunchly Catholic rule was overthrown – and now the centre of the secular republic.

The choice of the site, a symbol of the French republic to many, was criticised by supporters of France’s strict legislation separating church and state in public life.

But cheers rang out in the crowd as the pope thanked ‌God in his homily for the chance to ‌visit France on a whirlwind four-day, three-city tour to promote Catholicism and its teachings.

It is the first official papal visit to France in 18 years.

Pope Leo asked those in the crowd not to keep their faith to themselves. “Let it overflow, so that those you meet may be refreshed and their thirst satisfied,” he said. “From this beautiful city of Paris, I pray fervently that the living water of the Holy Spirit may flow throughout France.”

He told Catholics that only their faith, and not material things, can provide true happiness.

“Only God can fill the emptiness within us,” he said.

The security zone for the event – the biggest of the papal tour – stretched about 1.4 miles (2.2km), shutting down road traffic in central Paris from the Place de la Concorde to the Arc de Triomphe and beyond.

Chanting “Leo, Leo” and “Long live the pope”, crowds of people waved French and Vatican flags as the pontiff rode slowly down the grand boulevard of the Champs-Élysées aboard a popemobile – a specially designed, partly open vehicle used during public appearances.

He stopped frequently along the way as babies were lifted out of the crowd and brought to him to receive a papal caress on their heads. The city centre was sealed off for the service, with helicopters circling overhead and snipers positioned on rooftops.

About 14,500 police officers, gendarmes, military personnel and firefighters were deployed to the event, which was attended by 2,400 priests and deacons, and about 100 bishops.

Marie-Élisabeth, a 44-year-old nun from Burgundy, told a reporter for France 24: “This event is a way for us to say loud and proud that Christians are here.”

Speaking to reporters from Agence France-Presse, Sylvie Leclerc, a 51-year-old teacher, also said she and her fellow Christians want to share their fervour for their faith. “You don’t hear much from us Catholics, but now we’re going to make some noise!” she said. “But to proclaim love, peace, joy.”