Pope Benedict, wrapping up his visit to Australia, on Sunday urged a huge crowd of young people (picture) to beware the spreading "spiritual desert" that often accompanied modern prosperity.

At the start of his last full day in the country, the pope flew by helicopter over hundreds of thousands of pilgrims who staged an all-night vigil at a race track ahead of the outdoor papal Mass which formally ended World Youth Day celebrations.

"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," he said in his homily.

Some 200,000 young pilgrims camped out at the race track overnight, singing as temperatures dipped to about 8 degrees Celsius (46F). The crowd swelled to more than 300,000 as local residents flocked to the track on an overcast morning.

In a tribute to the region's native peoples, a group of dancers from South Pacific island nations danced in front of the pope in straw clothing that was in stark contrast to his traditional red and gold vestments.

But the pope's message to the young people was very traditional -- they had to avoid that "falsely conceived freedom" and look for that "underground river" of Christian values that will help them build their lives on firm foundations.

His underlying message to them over the past five days has been that they should have the courage to be Catholic and live the tenets of their religion openly and proudly.

The 1.1 billion-member Catholic Church hopes World Youth Day, the brainchild of the late Pope John Paul II, will revitalise the world's young Catholics at a time when the cult of the individual and consumerism have become big distractions in their lives.

The 81-year-old Benedict announced that the next one will be in Madrid, Spain in 2011 and that he hoped to be there.

WOODSTOCK, CATHOLIC SYTLE

It has been called the Church's version of Woodstock, five days and nights of peace, love and Christianity. More than 165 concerts have been staged, from religious music to heavy metal, acid jazz, and rap, along with mass confessionals and prayer meetings.

"This has been really cool," said Taylor Law, 19, who is about to enter university in his home town of Galveston, Texas, and who spent the night on the field with some 50 friends.

"Some of the countries the kids are from are in conflict but they are still here, showing that they are Catholic, that they believe in God as much each other does and this can only help peace," he said, waving an American flag as the Mass ended.

But this World Youth Day has been somewhat overshadowed by the issue of sexual abuse of minors by clergy.

Benedict on Saturday apologised directly for the first time for sexual abuse of minors by Catholic clergy, but victims groups in Australia said they wanted action and not words.

The pope, making some of his most explicit comments on the sexual abuse scandal that has rocked the Church in several countries, also said unequivocally that those responsible should be brought to justice.

In his homily at Sunday's concluding Mass, the pope made an oblique reference to the scandal, saying the Church needed "renewal," but in his comments welcoming the pope, Sydney's Cardinal George Pell was more direct.

"Too often she (the Church) is weighed down and burdened with the sins and failings of her children; too often she appears disfigured and discouraged," Pell told the pope.

Broken Rites, which represents abuse victims in Australia, has a list of 107 convictions for church abuse, but says there could be thousands of victims as only a few cases go to court.

In Australia, home to the world's biggest gay and lesbian mardi gras, the Church's teachings often fall on deaf ears.

More than 5 million Australians describe themselves as Catholic, but less than 1 million attend Sunday Mass and the number may have dropped to about 100,000 in the past 5 years.

Around 1,000 protesters marched in Sydney on Saturday against Church teachings on sexual morality, trying to hand out condoms to pilgrims who were marching to see the pope.

The pope, who appears to be holding up well despite the long trip, leaves for Rome on Monday.