Pope Benedict XVI called Latin America the "continent of hope" in an open-air mass at Brazil's most holy shrine Sunday and urged bishops to be zealous missionaries to reverse Catholicism's declining influence in the region.

In the city of Aparecida, as hundreds of choir members sang hymns and the faithful waved flags from all corners of South America, the Pope said the region's bishops must be "courageous and effective" to ensure the future strength of the church.

An aerial view shows the nearly 150,000 people who gathered for Pope's open-air mass Sunday at Brazil's largest cathedral, in Aparecida.
(Juca Varella, Agencia Estado/Associated Press)

"This is the faith that has made Latin America the continent of hope," Benedict told the crowd of nearly 150,000 gathered outside the mammoth Basilica of Our Lady Aparecida.

The turnout fell far short of the 400,000 to 500,000 worshippers local organizers had hoped would show up for Benedict's last public event on a five-day trip in Brazil, the largest Roman Catholic nation in the world.

Before heading back to Rome Sunday night, Benedict was expected to address the bishops again as they opened an important two-week regional conference, laying down his strategy to combat defections by the millions of Catholics who have been joining evangelical Protestant churches in recent years.

The church also faces huge challenges to its moral code in Latin America, as traditionally Catholic populations flout its prohibitions on abortion, divorce and premarital sex.

The issue is crucial for the Vatican.

While Latin America's largest nation is home to more than 120 million of the world's 1.1 billion Catholics, Brazil's census shows the percentage of citizens characterizing themselves as Catholics plunged to 74 per cent in 2000, from 89 per cent in 1980. The ranks of those calling themselves evangelical Protestants rose to 15 per cent from seven per cent.

Benedict said the church was not a political ideology or a social system.

It was an apparent reference to his vehement opposition to the liberation theology movement in Latin America that he moved to crush while he was a cardinal working for his predecessor, John Paul II.