Sydney - Up to 200,000 pilgrims were Saturday trudging Sydney's streets on their way to the papal mass that caps a youth festival stirring hearts in Australia's biggest city.

For only the third time in its 76-year history, the iconic Sydney Harbour Bridge was closed to vehicles for the day as marchers from 170 countries walked the 9-kilometre route from one side of the waterway to a racecourse where they will unroll their sleeping bags and spend a night under the stars.

Among those toiling on the three-hour slog was 22-year-old Hong Kong resident Peter Mok, who waved the Chinese national flag and laboured under a backpack almost the same size as himself.

"The highlight so far was the education expo because I want to go to a Catholic university in Australia," Mok said. "The other best thing was a Holy Trinity T-shirt I got that is green."

The mass closes a World Youth Day that opened in style on Thursday with the German-born pontiff sailing down the harbour to a former cargo wharf to be greeted by gleeful members of his global 1.2 billion flock.

The 81-year-old pope, who leaves on Monday, earned plaudits for a apology to Australians sexually abused by priests.

He spoke of "the shame which we have all felt as a result of the sexual abuse."

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

The apology was welcomed by John Hennessey, a spokesman for victims of abuse.

"He didn't have to use the words shame and betrayal and he used the words compassion and care," Hennessy said. "This is the sort of language that we love to hear. I sincerely congratulate His Holiness for being brave enough to show leadership to the world that he's not going to put up with this any more."

Melbourne schoolgirl Vanessa Potts, 16, was on the road early to reserve a spot as close to the pope as possible. Her mental scrapbook is crammed with images of camaraderie. Catholics in avowedly secular Australia are often teased about their religious observance, she said.

"You feel stronger in your faith, not ashamed of it or anything," Potts said. "I think the best thing was when the pope was in his boat and it sailed under the Harbour Bridge and we could see it and they all went mad."

Organizers reckon as many as 500,000 could attend the two-hour mass they said would seal the success of an event held somewhere in the world every three years.

Sydney residents who had moaned about the taxpayer funding and the traffic disruption have been won over by the untrammeled joy of the youngsters. Anticipated protests calling attention to the church's teachings against homosexuality, against priests marrying, against contraception and against women joining the clergy were largely drowned out by the more positive effects of the event.

"It's every bit and more than we dreamed of," said chief organizer Danny Casey. "The pilgrims, they think they are in paradise." (dpa)