Pope Francis, a champion of the poor and social justice, called on the faithful to reject today's consumer society at a huge open-air mass Thursday in Bolivia, South America's poorest nation.

On the second stop of his three-nation tour of South America, the pope addressed a throng in the vast Christ the Redeemer Plaza in Santa Cruz, including many people who camped out over night to see him.

He denounced what he called a "mentality in which everything has a price, everything can be bought, everything is negotiable. This way of thinking has room only for a select few."

"Jesus speaks these words to us, here in this square. No one has to be discarded," the 78-year-old pontiff, the first pope from Latin America, told the faithful.

Society cannot ignore people, the pope said, "no matter how little they possess or seem capable of contributing."

Since his election in 2013, Francis -- who hails from Argentina and is also the first Jesuit pope -- has indeed shown himself to have a down-to-earth air about him, and that is ringing clear in Santa Cruz.

He and several bishops are reportedly using a Burger King restaurant as their sacristy -- the place where they don their vestments and make other preparations for mass.

Many people spent the night in the plaza to get a spot for mass and a good view of the pontiff. The weather was unseasonably chilly, but was expected to warm as the day progressed.

"We want to be as close as possible to receive the blessings that he is going to bestow," said one of the happy campers, Nancy Camacho, her head wrapped in a thick scarf, before the service started.

Around the plaza, dominated by the giant bronze Christ the Redeemer statue, big-screen TVs were erected for people to watch the religious service.

Other highlights of the pope's visit to Bolivia include a visit Friday to an atrociously overcrowded prison where small children live with their parents, and a meeting with civic groups representing landless farmers, people working in the underground economy and activists opposed to globalization.

Francis arrived in Bolivia on Wednesday evening in the high-altitude Andean city of La Paz -- more than 4,000 meters (13,000 feet) above sea level.

Concerned authorities had extra oxygen tanks on hand for the pope, who lost a lung during his youth, but he was not seen using it.

He will head on Friday to Paraguay, the last stop on his tour of South America, which began in Ecuador.

- A robust pontiff -

Francis has impressed people with his stamina as he walked amid crowds, kissed people and took selfies. Some of the journalists traveling with him had to stop and take a shot of oxygen.

The pope came to the continent continuing to push one of the central themes of his papacy: social justice.

Bolivia is destitute -- the minimum monthly wage is equivalent to about $240 a month -- but has made economic progress in recent years.

"Bolivia is taking major steps to include broad sectors in the economic, social and political life of the country,' said the pope, who was welcomed by Evo Morales, the country's first president representing the indigenous majority.

Alcohol sales and musical performances have been banned throughout Bolivia during the pope's visit, and 17,000 police and soldiers have been deployed.

Before leaving for Paraguay on Friday, Francis will visit the huge Palmasola prison, scene of violent gang fighting in 2013 that left 31 people dead.

The prison is home to 120 children who live with their parents. That is illegal, but the government does not know what to do with the children. Some of the kids are as young as six.

The prison was built in the 1970s to house 600 people. It now has an astonishing 4,800 inmates.

All three of the countries Francis is visiting are predominantly Catholic and have been marked by a long history of poverty and inequality mostly afflicting indigenous populations.

The last visit by a pope to Bolivia was a six-day tour by John Paul II in 1988.