An estimated three million people are thought to have taken part in more than 100 protests across Brazil on Sunday in what the country's top newspapers hailed as the largest political demonstrations there ever.
The mass outcry is over Brazilian President Dilma Rousseff, who is facing a growing backlash amid the worst recession in decades and a sprawling corruption investigation that has closed in on key figures in her Workers' Party.
Sao Paulo streets were jam-packed with protesters.
Authorities in Sao Paulo, Brazil's biggest city and an opposition stronghold, said as many as 1.4 million protesters took part with many focusing their march on Paulista Avenue.
Corruption allegations a problem for former president.
A giant inflatable doll known as Pixuleco, depicting Brazil's former President Luiz Inacio Lula da Silva, took to the sky over Sao Paulo on Sunday. There was also a giant yellow duck.
Among other issues, federal investigators are trying to determine if Silva sold his influence in the current administration
in exchange for speeches and donations to his non-profit foundation Instituto Lula.
Rousseff has so far refused to resign.
Rousseff, who gathered her closest advisors for a Monday morning meeting in the Planalto presidential palace, categorically ruled out resigning last week. She said it was objectionable to demand the resignation of an elected president without concrete evidence the leader had violated the constitution.
Impeachment proceedings are expected to begin this week.
Lower house Speaker Eduardo Cunha, a Rousseff foe, is expected to form a commission to begin impeachment proceedings sometime this week.
"Surprised by the strong turnout on Sunday, the government has been put on alert that it needs to act quickly" to avoid Rousseff's impeachment, a report in the newspaper Folha said Monday.
Sunday's protests may have been the largest ever in Brazil.
Sunday's anti-Rousseff demonstrations are thought to have been larger than the mass protests in 1984 that called for direct presidential elections amid the country's former military dictatorship.
No major incidents, 'peaceful character' at protests.
The demonstrations, overwhelmingly comprised of the white, older middle-class people who have railed against Rousseff for years, may have weakened the government but they don't seem to have strengthened the opposition.
No major incidents were reported in Sunday's protests. The government highlighted "the peaceful character" of the demonstrations in a statement late Sunday, saying they underscored "the maturity of a country that knows how to co-exist with different opinions and knows how to secure respect to its laws and institutions."