The final event of the World Youth Day is under way, with Pope Benedict XVI taking the stage before an estimated crowd of up to 500,000 people to celebrate mass in Sydney.
The two-hour Papal mass at Royal Randwick Racecourse on Sunday was expected to attract the largest crowd ever assembled in Australia, according to WYD organisers.
Large television screens have been up and millions of people from around the world are expected to tune in.
The 81-year-old pontiff had a bird's eye view of the enormous crowd when he flew over the racecourse in a helicopter in the morning.
About 235,000 young Catholics had joined him in a vigil at the venue on Saturday night, having lugged sleeping bags and blankets on a 9km pilgrimage before sleeping under the stars.
Tens of thousands more joined them on Sunday morning ahead of the mass, which began at 10am local time.
After the Pope opened the service with a prayer, Sydney Archbishop Cardinal George Pell addressed the faithful.
Dr Pell said the church was rejoicing, adding that as he looked upon the "vast congregation" at Randwick it was obvious "the church is alive, and the church is young."
After the mass, the Pope will announce the next city to host an international World Youth Day in two or three years.
The mass will be followed by a concert for pilgrims.
Apology to sex abuse victims
On Saturday, the Pope apologised to people sexually abused by members of the clergy in Australia.
He raised the issue during a ceremony to consecrate the altar of St Mary's Cathedral in Sydney on Saturday, where he has been participating in World Youth Day activities.
"Here I would like to pause 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.
"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.
"These misdeeds, which constitute so grave a betrayal of trust, deserve unequivocal condemnation. They have caused great pain, they have damaged the church's witness."
The Pope called on his audience of 3,400 people, including Sydney Archbishop Cardinal George Pell, bishops, seminarians, and religious and school groups, to work together in "combatting this evil".
"Victims should receive compassion and care, and those responsible for these evils must be brought to justice," he said.