Pope Benedict XVI arrived in Sydney on Sunday to preside over a mammoth meeting of Catholic youngsters from around the world this week, dpa reported.
The pope's Alitalia Boeing 777 airplane touched down at a military base where Prime Minister Kevin Rudd and Cardinal George Pell were waiting to greet him.
The 81-year-old pontiff planned to rest for three days in a rural retreat outside Sydney before making a grand entrance on Sydney Harbour in what's been dubbed a "boat-a-cade."
Up to 500,000 could be at the closing mass July 20 that ends the pope's visit and the World Youth Day celebrations.
World Youth Day, begun in Rome in 1986, is held somewhere in the world every three years. Cologne, Germany, was the last host.
Organizers expect 125,000 to arrive in Sydney from abroad to join 100,000 Australian pilgrims.
Pope Benedict told reporters travelling with him from Italy that sexual abuse was "incompatible" with being a priest.
"It must be clear, that being a real priest is incompatible with (sexual abuse) because priests are in the service of our Lord," the pope said. "It's essential for the church to reconcile, to prevent, to help and to see guilt in this problem."
There was wide expectation that on his first visit to Australia the pope would repeat the apology to those who suffered sexual abuse from the clergy he made during his April visit to the United States.
Cardinal Pell, the archbishop of Sydney and leader of Australia's 5 million Catholics, said last week that an apology from the pope would be a "welcome contribution" at celebrations that open officially on Tuesday.