Pope Leo has called on French bishops to root out the "scourge" of sexual abuse in the Roman Catholic church, urging them to "maintain the greatest vigilance".

The Pope delivered the message to bishops during a private meeting at the Sanctuary of Our Holy Lady of Lourdes, a holy site in southern France, on the third day of his four-day official visit to France.

A 2021 inquiry found that clergy or lay members of the Church had abused about 330,000 people as children in France over 70 years.

The Pope said Mass in front of thousands of worshippers in Lourdes before later meeting survivors of abuse.

The Pope told the bishops: "You have faced with determination the painful scourge of abuse of minors committed by members of the clergy or within an ecclesial context.

"It is important to persevere along the path you have begun, maintaining the greatest vigilance."

The gathering of senior church leaders was held behind closed doors and the remarks were later released to reporters.

Leo then met with seven survivors of abuse by the French clergy.

The Pope "thanked them for their painful testimony and reaffirmed his commitment to ensuring that the harm they experienced is not repeated for others", the Vatican said in a statement.

"It was extraordinary," said survivor Jean-Marie Delbos at a news conference following the encounter with the pontiff. He said Leo listened and was informed of their cases. "I never thought I would have a Pope before me," he added.

The Lourdes gathering came a day after an estimated 700,000 people flocked to the Place de la Concorde in Paris to hear the pontiff speak.

Huge crowds cheered and waved as he rode down the Champs-Élysées Avenue greeting followers from his open-topped popemobile.

On Friday, the Pope also met French President Emmanuel Macron.