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The major events - Pope Benedict XVI's tour of Sydney on Thursday, the Stations of the Cross on Friday and the papal Mass on Sunday - are tipped to attract up to 500,000 people.
Pope Benedict XVI arrived amid tight security at a Royal Australian Air Force
base yesterday as thousands of young Catholic "pilgrims" flooded Sydney airport on their way to this week's World Youth Day.
The 81-year-old Pontiff waved briefly as he walked down the steps of the Alitalia "Shepherd One" at the end of a flight lasting almost 20 hours.
But it was his second touchdown in Australia - his plane made a short stopover in Darwin before continuing on to the Richmond Air Force Base on the outskirts of Sydney.
Crowds lined the Stuart Highway near Darwin airport to watch the Pope make his first Australian landfall. Bishop Eugene Hurley presented him with a painting of an Aboriginal Madonna and child.
At Richmond, he was welcomed by Prime Minister Kevin Rudd, New South Wales Premier Morris Iemma, federal and state ministers, and church dignitaries.
Travelling with the Pope were 24 Vatican officials and assistants and 43 members of the Vatican press corps.
The official welcome will be on Thursday, when hundreds of thousands of pilgrims and Sydneysiders are expected to jam the city centre.
Yesterday, the Pope and his party were driven in a motorcade to an Opus Dei retreat.
In an official message marking the visit, Pope Benedict described Australia as the "great southern land of the Holy Spirit" and said his heart reached out to all Australians.
He told reporters on board Shepherd One that he intended to apologise during his visit for sexual abuse by priests, as he had in the United States in April.
He said it was essential the church reconcile, prevent, help and see guilt and to make clear that the priesthood was incompatible with abuse.
The apology will come as the Australian church agonises over another scandal.
Cardinal George Pell of Sydney has ordered an inquiry into allegations against Father Terence Goodall.
The victim, Anthony Jones, has claimed the cardinal tried to cover up the abuse.
The Federal Court in Sydney will today rule on the legality of laws passed for World Youth Day, banning protesters from "annoying" pilgrims.
More than 100,000 foreign pilgrims, and a similar number of Australians, will attend World Youth Day events.