The final event of Sydney's World Youth Day is underway with Pope Benedict XVI taking the stage before an estimated crowd of up to half a million people to celebrate mass.

VIDEO: Pope prepares to hold Mass at Randwick

PHOTO GALLERY: World Youth Day Papal Mass

BLOG: The young and the pious

VIDEO: Pilgrims trek for Jesus

IN-DEPTH: World Youth Day

After the pontiff opened the service with a prayer Sydney Archbishop Cardinal George Pell addressed the faithful.

He said the church is rejoicing today and as he looked out over the vast congregation at Randwick he said it's obvious the church is alive and the church is young.

He said the church proclaims the Lord Jesus and she has no other task no other agenda no other mission.

But as she makes her way through history in the ancient lands of the Mediterranean or the new frontiers of the Pacific, Cardinal Pell said too often the church is weighed down and burdened with the sins and failings of her children.

‘Church alive with energy’

He said that at World Youth Day the church appears as she truly is alive with evangelical energy.

Dr Pell said the week of World Youth Day events has invigorated the faithful and he hopes that new outpouring continues from Sydney to the ends of the earth so they might all be more
faithful witnesses to Lord Jesus Christ.

He also thanked God for the fine weather of the past week and prayed for rain in the many parts of Australia still suffering from drought.

During the mass the Pope will confirm 24 Catholics.

It's due to end about midday.

Bird’s eye view of pilgrims

The pontiff had a bird's eye view of one of the nation's biggest gatherings earlier this morning when he flew over Royal Randwick Racecourse in a helicopter.

More than 230 thousand young Catholics had joined him in a vigil there last night and many stayed on for a chilly night out under the stars.

They were joined by tens of thousands more this morning.

The Pope did a lap of the racecourse in his popemobile this morning and as the slow-moving motorcade neared its end a baby was passed to the Holy Father, who kissed and blessed the child.

Security was tight along the motorcade’s route and security stopped flags from being shown.