Brazil's "pop-star priest" is already packing in the crowds at the newly opened mammoth sanctuary that he built for his campaign to stem the exodus of faithful from the Roman Catholic Church in Latin America's biggest nation.

Brazil still has more Catholics than any other country in the world, with about 65 percent of its 192 million people identifying themselves that way in the 2010 census. But that is down from 74 percent in 2000 and is the lowest since records began tracking religion 140 years ago.

That's where Father Marcelo Rossi's Mother of God sanctuary comes in. The not-yet-finished structure will seat 6,000 people and have standing room for 14,000 more, church leaders say. In addition, the grounds outside can hold 80,000 people who could watch Mass on outdoor video screens.

After the inaugural Mass on Friday attracted upward of 50,000 people, a beaming Rossi told reporters: "They couldn't all fit in. There was a crowd that had to stand outside! That's a sign we're on the right path, and it's this sanctuary."

Similar numbers jammed into the huge church Saturday.

It's a fitting stage for Rossi, a Latin Grammy-nominated singer who is known for tossing buckets of holy water on worshippers and performing rollicking Christian songs backed by a blasting live band during Mass.

The church sits on 323,000 square feet (30,000 square meters) of land. Church officials declined to confirm how big the actual building is, though local reports put it at 91,500 square feet (8,500 square meters). That would make it one of the world's 10 biggest churches. A cross soaring 138 feet (42 meters) into the air is the focal point.

The Mother of God sanctuary is anything but traditional. Designed by noted Brazilian architect Ruy Ohtake, it has a wide-open layout giving it the feel of a warehouse. Concrete walls hold up a sloping blue roof that from the outside looks more like a basketball arena than a house of worship. With the church several years away from completion, white plastic chairs were in the place of pews for a lucky few thousand to grab a seat. The rest had to stand.

Rossi dismisses the idea his huge church is a response to the explosion of the evangelical Christian faith in Brazil. Rather, the priest seems to be battling what recent studies indicate is Catholicism's biggest enemy: indifference.

While millions of Brazilian Catholics joined Pentecostal congregations in the 1990s, a study conducted last year by Brazil's Getulio Vargas Foundation based on census data found that the Catholics leaving the church these days are mostly becoming nonreligious. Experts have said the trend of Brazilians deciding organized religion isn't for them poses a more potent threat to Catholic leaders than losses to the Pentecostals.

Rossi chose to open his new church on the Brazilian holiday of Finados, the nation's version of the Day of the Dead. "A day, a day that was dead, was transformed!" the priest told worshippers during the service, using his gold-plated microphone.

The "pop-star priest" is seen by Brazilian Catholicism as its biggest weapon against the lack of interest, and his new sanctuary adds to his tools of best-selling books and music recordings to keep worshippers interested in what many complain has become a staid institution.

There was nothing stale about his Mass on Friday.

Singing as loud as they could, waving white hankies and swaying with a rocking band, the 20,000 people who jammed into the Mother of God sanctuary hammed it up for TV cameras and shed tears down their cheeks as their superstar priest waved to them from the pulpit. An estimated 30,000 other people had gathered outside, where young boys climbed up into nearby trees trying to get a glimpse of the church grounds as they squinted over a sea of heads streaming out of the sanctuary.

"We have problems, everyone has problems," worshipper Zuleima de Oliveira Sales said as she stood in the tightly packed sea of people under the soaring blue roof of the structure, her voice choking. "They don't come to an end, but I have faith, I have faith in Our Lady."

That's the sort of belief the Catholic Church is counting on in Brazil and other developing nations. Leaders from the Vatican on down are looking to them as bulwarks against losses in Europe and the U.S., where sex abuse scandals have inspired many people to leave the church. About half of the world's Catholics live in Latin America.

Pentecostalism was once seen as a major threat to Brazil's Catholic Church. Pentecostal churches, many of them founded by U.S. evangelicals, saw their membership double to more than 12 percent of the country's population over the 1990s, with about half of the congregants estimated to be former Catholics.

During the 1990s, Brazil's economy suffered from hyperinflation and other woes, and Pentecostal churches aggressively recruited in the slums and poor outskirts of Brazil's cities by offering nuts-and-bolts self-improvement advice as well as Christian ministry.

Since 2003, however, Pentecostal churches have seen growth slow. The percentage of Brazilians calling themselves Pentecostals edged up from 12.5 percent of the population to 13.3 percent.

Yet the Catholic Church has continued to lose parishioners, and church leaders have had little success so far in halting that trend.

Brazil was the first nation outside Europe that Pope Benedict XVI visited, during a five-day tour in 2007 largely aimed at stopping losses in Latin America. During the trip, the pope canonized Brazil's first native-born saint.

Then Benedict announced last August during the church's World Youth Day, which drew 1.5 million people to Spain, that the next version of the gathering would be held in Rio de Janeiro in 2013. The pope is expected to attend.

For now, Rossi hopes his big church will bring together tens of thousands of faithful for every Mass, giving new energy to the Catholic faith.

"People want big spaces. They want grand places for prayer," he told the Globo TV network. "One candle illuminates, 10 candles illuminate — and 100,000 candles light up so much more."