Pope Leo XIV presided over a final mass in Rome for over one million young people on Sunday, the culmination of a youth pilgrimage that has drawn Catholics from across the world.

"Aspire to great things, to holiness, wherever you are. Do not settle for less," Pope Leo told the young people during his homily.

The week-long pilgrimage ending on Sunday, a highlight of the Jubilee holy year, was an enormous undertaking for the Vatican, with half a million young pilgrims in Rome for most of the week.

On Saturday night, before a twilight vigil led by the pope, organisers had confirmed the attendance of 800,000 people in the vast, open-air space on Rome's eastern outskirts, and on Sunday the Vatican said that number had grown to one million people.

Most of those attending slept on the ground overnight in tents, in sleeping bags or on mats in anticipation of Sunday's mass.

In his homily, the first American pope and former missionary encouraged the gathered youth to "spread your enthusiasm and the witness of your faith to everyone you meet".

The Vatican has sought to highlight pilgrims who managed to travel to Rome from war-torn regions, with Leo saying on Sunday the Church and the world's youth were with them in solidarity.

"We are closer than ever to young people who suffer the most serious evils, which are caused by other human beings," he said in his Angelus, speaking in English.

"We are with the young people of Gaza. We are with the young people of Ukraine, with those of every land bloodied by war," said the pontiff, 69.

"My young brothers and sisters, you are the sign that a different world is possible, a world of fraternity and friendship, where conflicts are not resolved with weapons, but with dialogue." (AFP)