After touching down in Rio de Janeiro's airport at 3:43 p.m. local time where a small group of people and a children's choir welcomed him, Francis' motorcade headed into the city where the crowds of cheering and waving people grew larger and larger, the Catholic News Service reported. Before long, the enthusiastic Brazilians were pressing against the pope's car in their efforts to touch him and security personnel responded by pushing them back, the news service said.
The throngs frequently brought the motorcade to a stop, and at one point Francis got out of his car and kissed a baby.
The news service said the pope's 13.2-mile ride took 44 minutes.
While Francis eschewed his bulletproof popemobile for the more proletariat Fiat, his safety is a major consideration and authorities have more than 28,000 police officers assigned to protecting him during his stay in the country.
Brazilian television reported that on Sunday police found a homemade bomb inside a bathroom at the sanctuary of Our Lady of Aparecida, where Francis is scheduled to visit Wednesday.
During his flight to South America, the pontiff told reporters he was concerned about the future of an entire generation of youths unable to find work because of the global economic crisis. Francis said the economic situation could mean "we have the risk of having a generation that did not have work," Vatican Radio reported.
"Young people today are in crisis," the pope told reporters. "The possibility to earn one's daily bread, and gain personal dignity, comes from work," Italian news service ANSA reported.
The pope's remarks have particular relevance to Brazil, where he will take part in events marking World Youth Day. Joblessness among Brazilian youths has risen to 20 percent, the U.S. Agency for International Development says. In northern parts of the country, the unemployment rate among young would-be workers is 52 percent.
His concerns contrasted with a Twitter message he was "already full of joy" as he left Rome on his first trip outside Italy since becoming the leader of the Catholic Church in March.
His itinerary calls for visits to various sights in Catholicism's most populous country.
"This is an important visit," the Rev. Valdir Lima told USA Today after celebrating Sunday mass in Rio de Janeiro. "We need renewal."
Evangelical Protestant groups have made big inroads in Brazil, and the country has become more secular amid economic growth.
Fifty-seven percent of Brazilians consider themselves Catholic, down from 75 percent two decades ago, a poll released Sunday by Datafolha, a Brazilian research company, indicated.
In 1980, when Pope John Paul II made the first visit by a pope to Brazil, nearly 90 percent of the population considered itself Catholic.
Protestants rose from 6 percent to 22 percent between 1980 and 2010.
Throughout Latin America, people identifying themselves as Catholic fell to 72 percent in 2010 from 90 percent in 1910, the Pew Forum on Religion and Public Life reported in February.
Still, Brazil remains the world's largest Roman Catholic country and Latin America accounts for 39 percent of the world's Catholics.
Experts say developing regions such as Latin America and Africa, with fast-growing populations, hold the greatest hope of renewed growth for the church.
Francis, born in Argentina to Italian parents, is the first Latin American and the first Jesuit pope.
"A lot of people decided to come because the pope is Latin American," Cesar Jaya, a 20-year-old Ecuadorean Catholic, told The Wall Street Journal.
"It's our continent, he's our pope."
There is a homecoming feeling for the visit but security for the 76-year-old pontiff is a big concern, officials said.
The pope has a week of open-air events, including two mass celebrations on the 2.5-mile Copacabana balneario beach. The events are expected to attract up to 1.5 million people.
The visit comes a month after Rio and other Brazilian cities had more than a million protesters take to the streets.
The protests, which started June 20, were initially over bus-fare increases but quickly expanded into anger over political corruption, police brutality, the high cost of living and huge public spending for the 2014 FIFA World Cup soccer tournament at the expense of education.
The protests have quieted down in most cities but continue in Rio where they sometimes end in violence.
Francis has endorsed the protests in general terms and was expected to convey sympathy for the protest demands and those involved in the movement this week.
"The pope will certainly have words about the issues the young people have raised, their dissatisfaction or searches, but also their great desire to participate in change," Sao Paulo Archbishop Cardinal Odilo Pedro Scherer was quoted by The New York Times as saying.
Francis intends to focus on the gospel of social justice he has said he wants to make the focus of his papacy, the Times said.
The pontifical visit was originally planned for Benedict XVI, Francis' predecessor, who announced the event at the end of the last World Youth Day two years ago in Madrid.
At Francis' request, the original itinerary was expanded to include a visit to Aparecida, site of Brazil's biggest shrine to the Virgin Mary.
It was also there, during a visit by Benedict in 2007, that Francis, then Cardinal Jorge Mario Bergoglio, presided over the writing of a policy document presented to the pope on behalf of the Latin American Episcopal Conference.
The document emphasized social justice and evangelization.