* Over 150,000 expected for mass at shrine to Virgin Mary
* Authorities focused on security after raucous welcome
* Shrine was site of influential document penned by Francis
Pope Francis landed early Wednesday at a shrine in southeastern Brazil, where he will celebrate his first mass outside Italy as pontiff and seek to energize faithful in the country that is home to the world's largest Roman Catholic population.
On the third day of his week long visit for World Youth Day, a biennial Church gathering being celebrated in and around Rio de Janeiro, Francis will preach to faithful in Aparecida, Brazil's most important Catholic shrine.
More than 150,000 people are expected to attend the service about 162 miles (260 km) west of Rio, a locale long venerated in Brazil as a shrine to the Virgin Mary and site where Francis, as an Argentine cardinal during a 2007 visit by Pope Benedict XVI, cemented his place as a leader of the Church in Latin America.
The ongoing World Youth Day events, which are expected to attract more than 1 million people from around the world, are an effort by the Vatican to galvanize young Catholics at a time when rival denominations, secularism and distaste over sexual and financial scandals continue to lead some faithful to abandon the Church.
Francis, 76, arrived in Brazil on Monday to a wildly enthusiastic reception. His message of humility and rejection of the luxurious trappings used by papal predecessors have endeared him to many Catholics.
The pope's desire to be close to his flock, though, has complicated security around his visit, especially after he used a simple, four-door Fiat for his ride into Rio from the airport and insisted on using an open top vehicle to greet visitors during a welcome procession through the city center.
At one point on Monday, the Fiat's driver took a wrong turn into the uncordoned lane of a major avenue and exposed the pope to a swarm of well-wishers who surrounded the car and reached in through its open window.
On Wednesday, more than 5,000 police and other security officials are expected to be on hand in Aparecida, home to a terra cotta likeness of a Virgin considered the patroness of Brazil. Early in the day, young pilgrims, many draped in the flags of Brazil, Argentina, and other countries, endured rain and unseasonably low temperatures to ensure spots for the service.
After passing through metal detectors, the crowds of pilgrims waited to hear the pope say mass under a sea of umbrellas dotted with flags from Argentina and Brazil.
"I got here with my family at 2 in the morning," said Antonio Carlos da Silva, a drenched prison guard from Sao Paulo. "I am so happy to come and see the pope."
Francis, who was head of the archdiocese of Buenos Aires during the 2007 visit by Benedict to the shrine, authored an influential statement at the time that espoused many of the same values he has placed front and center during his five months as pope. The document called on the Church to return to the principles of humility and charity.
After his visit to the shrine, Francis is scheduled to fly back to Rio and tour a drug treatment ward at a hospital run by Franciscan monks. Later in the week, he will visit a Rio slum, preside over services on Copacabana beach and over the weekend give mass at a pasture outside the city.