Pope Benedict XVI has arrived in the Brazilian city of Sao Paulo for a five-day visit to the world's most populous Roman Catholic nation.
The pope travelled into downtown Sao Paulo after his arrival
It is his first visit to Latin America since becoming Pope in April 2005.
He is to perform a series of open air Masses before travelling to Aparecida for the focus of the visit, a major conference of Latin American bishops.
There he is expected to touch on the growing challenge the Catholic Church faces from evangelical groups.
10 May: Meets Brazilian President Lula in Sao Paulo, then Church leaders and young people
11 May: Pope leads prayers around Sao Paulo
13 May: Prayers and address to open Latin American bishops' conference at Aparecida
Talking to journalists on the flight, the Pope said his main concern in the region was the loss of millions of disaffected Roman Catholics to evangelical churches.
According to a recent study, some 64% of Brazilians are Catholic, but this number represents a 10% fall compared to 10 years ago and contrasts with an upsurge in converts to evangelical churches.
The issue of abortion is also expected to feature, amid dismay within the Catholic Church at Mexico City's move to legalise it.
'Peace to all of you'
Brazilian President Luiz Inacio Lula da Silva greeted Pope Benedict as his plane touched down at Sao Paulo's international airport.
"I extend my greetings to all the peoples of Latin America and the Caribbean in the words of the Apostle: 'Peace to all of you who are in Christ'," the Pope said, speaking in Portuguese.
Crowds waited in the rain to catch a glimpse of the pontiff, who later went to a monastery where he will stay during the visit.
At the monastery, the faithful chanted "Bento, Bento" as he arrived and waved flags as he blessed them.
On Thursday, he is to address a youth gathering in the city's Pacaembu stadium and on Friday canonize Brother Antonio Galvao, Brazil's first native-born saint, during a public Mass.
Then on Sunday, Pope Benedict is to open the bishops' conference, the first such meeting for 15 years.
The two-week forum will bring together almost 200 bishops and cardinals from across Latin American and the Caribbean to set out the Church's agenda and policies in the region for the coming years.
The conference comes only weeks after Mexico City's decision on abortion.
This is Benedict's first visit to Latin America as Pope
Talking to journalists on the plane, Pope Benedict appeared to back Mexico City church officials who said that politicians who supported the law and medical workers who performed abortions would be excommunicated.
A Vatican spokesman later clarified the issue, saying the Pope did not intend to excommunicate anyone.
However, Father Federico Lombardi said that "legislative action in favour of abortion is incompatible with participation in the Eucharist" and therefore "politicians exclude themselves from Communion".
The subject is also up for debate in Brazil. The health minister has recently said he would like to see discussion on abortion - currently permitted only in limited circumstances - a suggestion that has already prompted a vigorous response from senior clergy.
President Lula has already made it clear that he regards the question more as a matter of public health than a moral choice.
But our Vatican correspondent, David Willey, who is travelling with the Pope, says that the Church is reluctant for even a similar public discussion on the issue in Brazil.
The Pope said it was the issue of Catholics choosing to join evangelical churches that was "our biggest worry". "We need to find a convincing response," he said.
Pope Benedict is sure of a warm welcome from the Catholic faithful in Brazil, says the BBC's Simon Watts.
But his problems is that both he and the local Catholic hierarchy are more conservative than most Brazilians.
To the converts, the evangelicals offer the chance of redemption now, rather than in the after-life, as well as a social network and help with problems like drink or drugs.
In contrast, Catholic rituals can seem stuffy and out-of-touch with day-to-day reality for most Brazilians, our correspondent adds.