Pope Francis has encouraged Brazil's youth, who have protested en masse against corruption in their country over the last few weeks, to continue their efforts to change society by fighting apathy and offering "a Christian response".

The 76-year-old pope spoke to a crowd estimated by the Vatican to be more than 2 million people gathered on Rio de Janeiro's famed Copacabana beach for an evening rally on Saturday.

He also urged young people to shun fleeting fads and to become "athletes of Christ".

Francis, nearly concluding his first overseas trip, received yet another rapturous welcome when he arrived at the crescent-shaped beach. He stopped his popemobile several times to kiss babies and an Argentine flag that was waved at the car.

Most participants planned to spend the night on the sand and adjacent pavement to hold their places for Sunday's closing Mass on the same spot, making the place a giant campsite.

Brazil, Latin America's largest nation, was rocked by massive protests against corruption, the misuse of public money and the high cost of living. Most of the protesters were young.

Francis told the gathering he knew that young people had taken to the streets in Brazil and elsewhere "to express their desire for a society that is more just and fraternal".

Speaking from a giant white stage, he encouraged them to fight apathy and be "protagonists of change" and offer "a Christian response to the social and political concerns arising in many parts of the world".

Francis has dedicated much attention in his speeches to the problems, the prospects and the power of young people.

On Friday night he urged them to change a world where food is discarded while millions go hungry, where racism and violence still affront human dignity, and where politics is more

associated with corruption than service.

The day before, during a visit to a Rio slum, he urged them not to lose trust and to not allow their hopes to be extinguished. Many young people in Brazil saw this as his support for peaceful demonstrations to bring about change.