Sydney (AP): Pope Benedict XVI urged young people on Sunday to reject what he said was the ``spiritual desert'' spreading throughout the world and to embrace Christianity to build a new age free from greed and materialism.

At a Mass before some 350,000 young Roman Catholic pilgrims in Sydney, Benedict said ``the world needs renewal'' and challenged them to be the agents of change.

``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 pontiff said.

The 81-year-old pope said it was up to a new generation of Christians to build a world in ``which God's gift of life is welcomed, respected and cherished _ not rejected, feared as a threat and destroyed.''

The aim was ``a new age in which hope liberates us from the shallowness, apathy and self-absorption which deadens our souls and poisons our relationships,'' he said.

Sunday's Mass wrapped up the church's six-day World Youth Day festival in Sydney that has drawn massive crowds of pilgrims to Australia's largest city, and has been watched on television by a global audience estimated to be in the hundreds of millions.

Benedict announced that, as expected, Madrid, Spain, would host the next World Youth Day in 2011 and told the pilgrims: ``I look forward to seeing you again in three years' time.''

The Mass was delivered at a horse racetrack filled with pilgrims who had camped out overnight.

Spokesman Rev. Federico Lombardi said the Vatican estimated the crowd at 350,000. Organizers said many more watched on giant television screens around the city, and surmised a global television audience of hundreds of millions.

The pope flew over the scene early Sunday in a helicopter _ dubbed ``the holy-copter'' by bleary-eyed pilgrims below _ to see the assemblage swarmed all over the track in a jumble of sleeping bags, backpacks and other personal items.

He later took a slow drive through the crowd, stopping once to plant a kiss on the forehead of a toddler held up to the popemobile's window. Pilgrims from more than 160 countries gave him a rock-star welcome, waving the flags of their nations, cheering and chanting: ``Benedicto! Benedicto!'' _ the pope's Italian name.

Benedict, who shrugged off the effects of a longer-than 20-hour flight from Rome and kept a hectic schedule during his time in Australia, coughed a couple of times during Sunday's Mass and at one point blew his nose, prompting reporters to ask about his health.

``It was chilly, and everybody felt it, no?'' Lombardi said. ``But he is in fine health.''

The Mass comes a day after the pope made a forceful apology for the sexual abuse of children by Australia's Roman Catholic clergy, keeping up efforts begun in the United States to publicly atone for what he called evil acts by priests.

In his apology Saturday, Benedict said: ``I am deeply sorry for the pain and suffering the victims have endured and I assure them as their pastor that I too share in their suffering,'' Benedict said in Sydney's St. Mary's Cathedral.

He said he wanted ``to acknowledge the shame which we have all felt'' and called for those responsible to be ``brought to justice.'' The acts were ``evil'' and a ``grave betrayal of trust,'' he said.

But the pope's apology was not enough to satisfy representatives of the victims of clergy sexual abuse, who said it must be backed by Vatican orders to Australian bishops to stop what they say are efforts to cover up the extent of the problem and to block survivors' attempts to win compensation.

Sunday's events wrap up a busy four-day schedule for Benedict in which he touched on all the major themes of his three-year-old papacy, including the need to rejuvenate what he says is a church that is in ``crisis'' in the West because people were losing their faith in God.

He also stressed the need for mankind to protect the environment and end its ``insatiable consumption'' of the world's resources. He continued to reach out to other faiths, telling leaders of Islam and other religions they must unite against those who were threatening the world with ``sinister and indiscriminate violence.''

The pope was due to leave Australia for the Vatican on Monday.