A top state security official said that some 1.5 million pilgrims are expected in Rio late this month for Pope Francis' visit during a major Roman Catholic youth fest.
"According to the latest figures, we are expecting up to 1.5 million people" for World Youth Day (WYD) July 23-28," said Roberto Alzir Dias Chavez, the deputy security secretary for Rio de Janeiro state.
He added that he did not know if attendance was likely to be affected by nationwide social unrest that jolted Brazil last month.
Initially, organizers of the Catholic fest were expecting to draw two million people for the second WYD in Latin America, 26 years after the one held in Buenos Aires in the presence of then pope John Paul II.
With the surprise election of an Argentine pontiff, they even made plans for the arrival of up to 2.5 million pilgrims.
Last month, hundreds of thousands of Brazilians marched nationwide to demand better public services and an end to endemic corruption.
They also questioned why the government was investing billions of dollars in sporting events like next year's World Cup when education, housing and transport are underfunded.
Brazil boasts the world's biggest Catholic community -- 123 million out of a total population of 194 million.
But Catholics are facing a surge in the number of evangelical Protestants, from 26.2 million in 2000 to 42.3 million in 2010.