LISBON, Portugal (AP) — Hundreds of thousands of flag-waving young people from around the globe gave Pope Francis a raucous welcome to the World Youth Day festival in Portugal's capital Thursday, in a sign of youthful support for the 86-year-old pontiff and his calls for inclusivity and economic justice.

In a display of enthusiasm not seen since the early years of Francis' decade-old papacy, teenagers and young adults thronged a downtown Lisbon park for the opening ceremony of the Catholic jamboree. Pilgrims ran alongside as his popemobile made languid loops through the crowd and a smiling Francis basked in their cheers.

The pope, who was hospitalized twice this year, had said he hoped to be “rejuvenated” by his five-day trip to Portugal, and it appeared as if the sun-baked crowd delivered.

Organizers estimated some 500,000 pilgrims attended the music-and-dance filled World Youth Day opening ceremony in Lisbon’s Eduardo VII park, a figure that was expected to more than double during the festival's coming days.

Volunteers with huge water packs on their backs doled out water to keep the youngsters hydrated, an increasing concern given temperatures are expected to soar to 40 degrees Celsius (104 degrees Fahrenheit) by Sunday, when Francis closes out the festival with a final outdoor Mass.

Francis is in Portugal through the weekend to preside over the jamboree that St. John Paul II launched in the 1980s to encourage young Catholics in their faith. The Argentine Jesuit has picked up John Paul’s mantle with gusto as he seeks to inspire the next generation to rally behind his key social justice and environmental priorities.

On Thursday, he emphasized his call for the Catholic Church to be welcoming to all, sinners included. "There is room for everyone in the church," Francis told the crowd, leading the young people in a chant of “todos,” which is Spanish and Portuguese for “everyone.”

“I think he is a very modern pope. I like his thoughts on many things," Gaia Selva, 27, who traveled to Lisbon from Italy with a group of 374 members of the Salesian religious order and was in the park for the opening ceremony. "I hope his support can help us as youth but also others, to understand our religion better and to live it to the fullest.”

Maria Seybert, 19, of Littletown, Colorado, was attending her first World Youth Day and seemed inspired by Francis' exhortations to spread the faith.

“Yeah, I know that our church is very broken; we have a lot of sinners and broken people," Seybert said. “I desire to hear something that encourages us to recognize our poverty and woundedness, and then run with it.”

Many young Catholics around the world have embraced Francis’ core teachings about correcting economic injustices and promoting environmental custodianship, joining church-sponsored foundations and social movements under the banner of the “Economy of Francis” and the “Laudato Sii” movement, named for Francis’ 2015 encyclical on the environment.

Francis pressed those causes again Thursday, first at Catholic University, one of Portugal’s top institutions of higher learning, where he urged students to take risks and reject the temptation to merely perpetuate the status quo, or what the pope called the “present global system of elitism and inequality.”

“An academic degree should not be seen merely as a license to pursue personal well-being, but as a mandate to work for a more just and inclusive — that is, truly progressive — society,” he said.

Francis encouraged the students to use the privilege of their educations to protect the environment, care about poor and marginalized people, and to “redefine what we mean by progress and development.”

“Yours can be the generation that takes up this great challenge," he said. “We need to align the tragedy of desertification with that of refugees, the issue of increased migration with that of a declining birth rate, and to see the material dimension of life within the greater purview of the spiritual."

Francis next met with another group of students in Cascais, a beachside resort town, at the local branch of Scolas Occurrentes, a foundation he started years ago to bring young people from different backgrounds and nationalities together. Sitting in a brilliantly painted common room, Francis told them that a life without chaos or crises was like drinking distilled water: tasteless and “gross.”

“It's important to walk together, resolve crises together and go forward, growing,” he said.

As he left, popular singer Cuca Roseta serenaded him with a sentimental, a cappella fado version of “Ave Maria.” Along his motorcade route was a 3-kilometer-long (1.9-mile-long) banner that Scolas members had painted in honor of his visit.

Francis' visit to Portugal is aimed primarily at young people, but his message about reversing economic inequalities has found resonance among people of all ages, who lined his route and watched from hotel balconies or the street as his motorcade passed.

“It’s a big issue and more should be done about it,” Alison Morais, 42, a Brazilian immigrant who works as a store assistant in Cascais. “It’s hard to change it, but at least people listen to what (the pope) says and it gets the conversation going.”

Francis is scheduled Friday to visit some charities and hear the confessions of some young pilgrims before presiding over a Way of the Cross procession. He travels to the Catholic shrine in Fatima on Saturday and then celebrates an open-air vigil Saturday and final Mass on Sunday morning.

After arriving in Lisbon on Wednesday, the pope immediately addressed Portugal’s clergy sexual abuse crisis, which intensified after a panel of experts hired by the country's bishops reported in February that priests and other church personnel may have abuse at least 4,815 boys and girls since 1950.

Meeting with the bishops at Lisbon’s iconic Jeronimos Monastery, Francis said the “scandal” of sexual abuse had marred the face of the Catholic Church and helped drive the faithful away. He told the bishops that abuse victims must always be welcomed and heard.

The pope met for more than an hour that night with 13 victims at the Vatican Embassy.