The pilgrims are remaining in place for a Mass to be celebrated there by Francis later on Sunday.

In his address, he urged the pilgrims not to be part-time Christians but to lead full, meaningful lives.

The Pope, who has been attending the biggest ever Catholic World Youth Day, leaves Brazil on Sunday after five days - his first overseas trip as pontiff.

Speaking on a huge stage at the beach where a mock church structure was built, Pope Francis referred to the street protests which have been taking place in Brazil for more than a month.

"The young people in the street are the ones who want to be actors of change. Please don't let others be actors of change," he told the crowd at the vigil.

"Keep overcoming apathy and offering a Christian response to the social and political concerns taking place in different parts of the world."

By the time the Pope's car had reached the stage, the back seat was filled with soccer jerseys, flags and flowers thrown to him by adoring pilgrims lining the route.

The BBC's Wyre Davies in Rio says almost every inch of the two-and-a-half mile long beach was occupied as most of the young people stayed on, pitching tents or sleeping in the open.

As the crowd grew, female activists held a demonstration nearby in support of abortion and women's rights.

But our correspondent says the Pope and the Church hierarchy will be delighted at the huge turnout and the way Francis has been received by pilgrims from across the globe.

The Mass will be celebrated at the beach in the early afternoon.

Earlier on Saturday, the Pope addressed civil leaders and government officials at Rio's Municipal Theatre.

"Between selfish indifference and violent protest, there is always another possible option: that of dialogue," he said, in a reference to demonstrations that have been rocking the country since June.

"A country grows when constructive dialogue occurs between its many rich cultural components: popular culture, university culture, youth culture, artistic and technological culture, economic culture, family culture and media culture."

In the past three decades, the Catholic church has lost millions of followers to smaller Christian denominations.

Also on Saturday, the Pope repeated his challenge to fellow Roman Catholic clerics to take to the streets.

In a speech to 1,000 bishops and clerics in Rio's cathedral, he said they should go to the favelas - Brazil's shanty towns.

"We cannot keep ourselves shut up in parishes, in our communities, when so many people are waiting for the Gospel," he told the audience.

Protests, sometimes violent, broke out in cities across Brazil last month against corruption, poor public services and the high cost of events like the 2014 World Cup.