Pope Francis has told young people that the Catholic Church needs them and urged them to follow their dreams as he wrapped up World Youth Day in Portugal with a massive open-air Mass for an estimated 1.5 million people.

“Do not be afraid,” Francis told the vast crowd of pilgrims, many of whom camped out overnight on the Lisbon field so they could be in place for the grand finale of the Catholic festival.

The Vatican said that the estimated 1.5 million pilgrims were joined by 700 bishops and 10,000 priests.

During the event, he also announced the next World Youth Day, a major Catholic festival, will be held in Seoul, South Korea, in 2027. It will be the first time the festival has returned to Asia since 1995, when millions turned out for one of St John Paul II’s biggest events in Manila, the Philippines.

Before departing, Francis went to thank some of the event’s around 30,000 international volunteers.

They assembled at a riverside site despite the afternoon heat that reached around 40C (104F) and prompted authorities to issue an extreme weather alert.

The pontiff appeared uncomfortable in the heat as he toured the site in an open-topped popemobile, but was at ease as he gave a speech from a shaded stage.

Francis largely stuck to script on Sunday but again skipped much of his prepared homily, continuing the improvisation that has characterised his five-day trip to Portugal.

Early on in his 10-year papacy, Francis would frequently go rogue and ignore his pre-planned speeches, seemingly moved by the moment to engage directly with even huge crowds of people.

In more recent years, he largely stuck to script especially when visiting places where Christians are a minority or where his audiences might not appreciate his informal style.

But in Lisbon, he has been back on comfortable turf, with many people who can easily follow his native Spanish and seem to appreciate his conversational way of communicating. They also seem to appreciate the massive turnout.

“I never thought that so many people would come,” said Ana Garcia Prat, a 23-year-old Spanish pilgrim in Lisbon. “In my head, I never pictured a Mass with so many people from so many different countries.”

On Sunday, Francis urged the young people to follow their dreams and not be afraid of failing, reprising a theme that St John Paul II frequently repeated during his quarter-century of World Youth Days.

“As young people, you want to change the world and it is good that you want to change the world and work for justice and peace,” Francis said. “You devote all your energy and creativity to this, yet it still seems insufficient.

“The Church and the world need you, the young, as much as the Earth needs rain.”

“Do not be afraid!” he said.

After Francis announced Seoul would host the 2027 edition, South Korean youths bearing a huge national flag jumped on the stage in glee. Catholics represent 10% of South Korea’s population of 50 million.

Seoul Archbishop Peter Soon-taek Chung told reporters that he expected “hopefully” more than the around 300,000 pilgrims who attended the 2008 Sydney edition to come to Seoul.

He said one aim would be to reinvigorate youth ministry in South Korea, which he said had suffered during the pandemic with fewer young Catholics attending Mass.

Over the last few days, Francis has ditched speeches in favour of off-the-cuff conversations with young people and substituted a formal prayer for peace in Ukraine at the Fatima shrine, long associated with exhortations of peace and conversion in Russia. The Vatican later published part of the prayer on Twitter.

Responding to questions about whether the Pope’s health is the reason behind his ignored speeches, Vatican spokesman Matteo Bruni said Francis is in good shape and is not suffering any eyesight problems that would make reading his remarks difficult.

The young people seem thrilled with all the Pope has been saying and braved searing temperatures to hear him in person.

They woke on Sunday as the sun rose over the River Tagus. Many had slept on mats, cots and the bare ground to be in place for Francis’s Mass, scheduled for early to avoid midday temperatures that were expected to hit 40C. Starting at dawn, a priest-DJ started spinning thumping reggae and Christian hymns from the sound system.

Francis’s message this week has been one of inclusivity, insisting that “everyone, everyone, everyone” has a place in the church. That is consistent with his message that the church is not a place of rigid rules where only the perfect can be let in, but rather a “field hospital” for wounded souls, where all are welcome.

Lisbon Cardinal Manuel Clemente said the Pope wanted the event to be “open… to everyone, showing the breadth of the gospel, which excludes no-one and is open to all”.