The Pope launched a fresh assault on consumer culture and materialism today, warning of a “spiritual desert” spreading across the world in a speech to a sprawling, flag-waving crowd of about 400,000 worshippers at a mass in Sydney.

Benedict XVI, who yesterday apologised to children abused by paedophile priests, challenged young people to help build a “new age” by rejecting the “indifference, spiritual weariness and blind conformity” of the times. He also urged them to fill the growing gaps in the ranks of priests and nuns.

“A new generation of Christians is being called to help build a world in which God’s gift of life is welcomed, respected and cherished — not rejected, feared as a threat and destroyed,” the pope told the crowd, which the church claimed was the biggest on record in Australia.

Building on a theme he has developed over four days at the Catholic World Youth Day celebrations, Benedict used his final address to give a scathing assessment of the impact of secularism and the focus on material wealth.

“The world needs renewal…the Church also needs renewal,” he said during the mass at Randwick racecourse, with many worshippers nearly a kilometre from the giant stage.

“In so many of our societies, side by side with material prosperity, a spiritual desert is spreading: an interior emptiness, an unnamed fear, a quiet sense of despair.”

The Pope blamed the problem on the modern world’s “hard crust of indifference” to God. The world “wants to forget God, or even reject him in the name of a falsely-conceived freedom,” he said.

Instead, he called for a “new age in which hope liberates us from the shallowness, apathy and self-absorption which deadens our souls and poison our relationships.”

He also appealed to the young to give their lives to the task by joining the priesthood or sisterhood. If the calling came, he said, “do not be afraid to say 'yes' to Jesus”.

The crowd included 3,000 priests, 420 bishops and 26 cardinals and was full of pomp and ritual, with massed choirs, trumpet fanfares and kettle drums. More than half the crowd had kept a candle light vigil and braved a chilly winter night in their sleeping bags.

The Pope arrived by helicopter before transferring to his Popemobile for a tour of the crowded racecourse, pausing momentarily to bless three babies through the window.

Despite his tough message, he appeared to enjoy himself with a chuckle at the antics of Spanish supporters after he named Madrid as the next venue for the event in 2011.

After confessing that he had found the long flight from Rome daunting, Benedict said he had had an “unforgettable experience” in Australia, “this great southern land of the Holy Spirit”.

The 81-year-old pope appeared to connect well with his mostly youthful audience. But, while rapturously received, he sometimes struggled with pronunciation with his gentle German-accented English.

Australian Catholic leaders declared the festival a success, with more than 125,000 foreign pilgrims joining local worshippers for the event. There were big crowds at every event, from the Pope’s arrival by boat on Thursday to the re-enactment of the crucifixion along city streets on Friday.

Police reported virtually no trouble from the big, good-natured groups of young people from about 170 countries.

Despite yesterday’s huge show, the church faces a continuing struggle for survival with falling priest numbers and attendances. Most Sundays well under a fifth of the country’s 5 million Catholics go to church.

On Saturday, Benedict sought to heal the deep rift in the Australian church with his apology to children abused by priests. “I would like to … acknowledge the shame which we have all felt as a result of the sexual abuse of minors by some clergy and religious in this country,” the Pope said at St Mary’s Cathedral.

Departing from his written text, he then added: “Indeed I am deeply sorry for the pain and suffering the victims have endured and I assure them that, as their pastor, I too share in their suffering.”

Some victims groups welcomed the apology but others rejected it. They cited comments by Bishop Anthony Fisher, a World Youth Day organiser, as evidence that the Church did not “get” the issue of abuse.

Early last week Bishop Fisher described a report of a father’s anger over the church’s handling of the rape of two of his daughters by a priest in the early 1990s as “crankily dwelling…on old wounds”. One of the girls had committed suicide this year. The bishop said he was referring to the media, not the family.