SYDNEY - The Pope issued a powerful apology to victims of sexual abuse by Roman Catholic clergy, damning paedophile priests for their "evil" acts and insisting that they be brought to justice.

Pope Benedict XVI's apologised to Australian children who suffered sexual abuse at the hands of Catholic priests.

In his most strongly-worded statement yet on the crisis that has engulfed the church globally, Pope Benedict XVI strayed from a prepared homily and said:

"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," he said during a mass in Sydney, where he has spent the past week for World Youth Day celebrations.

"These misdeeds, which constitute so grave a betrayal of trust, deserve unequivocal condemnation. They have caused great pain and damaged the church's witness.

"Victims should receive compassion and care and those responsible for these evils must be brought to justice."

It is not the first time the Pope has acknowledged publicly the abuse of children by Catholic priests, but goes further than previous statements by making a specific apology and stating clearly that the perpetrators must be punished.

The apology was made at a mass attended mainly by priests and seminarians at St Mary’s Cathedral in Sydney.

The Pope's apology was made before the climax of World Youth Day, a papal mass on Sunday in front of up to half a million pilgrims at a racecourse in central Sydney.

Sydney Harbour Bridge was closed to traffic as young Catholics from around the world streamed across on foot, making the 5.5-mile trek to Royal Randwick Racecourse where they were to join the Pope for a two-hour vigil before camping out overnight.