Military police estimate one million Brazilians have taken to the streets in Sao Paulo to oppose President Dilma Rousseff, a target of rising discontent amid a faltering economy and a massive corruption scandal at state oil giant Petrobras.
Large protests were also held in other major cities on Sunday, with 20,000 demonstrators marching in the capital Brasilia, 15,000 on Copacabana beach in Rio de Janeiro and 4,000 in Salvador de Bahia, according to police estimates.
Al Jazeera's Adam Raney, reporting from Sao Paulo, said that the large crowds had turned out in force to voice their feelings about the direction of the country under Rousseff and the ruling Workers Party (PT).
"A large contingent of people are really angry. They are fed up with the scandal," Raney said, adding that the plunging currency was adding to the discontent.
Sao Paulo, the country's economic centre, is a stronghold of opposition to Rousseff.
Dressed in the yellow and green of Brazil's flag, many protesters demanded the impeachment of Rousseff who has just begun her second term after re-election at the end of 2014.
In Rio de Janeiro, people waved Brazilian flags along the coastal Copacabana avenue behind a truck blaring slogans against Rousseff.
"Out Dilma, out PT," people chanted.
A few protesters even called for military intervention to end the Workers Party's 12 years in power.
Construction contractor Alessandro Braga, 37, attended the rally in Brasilia with his wife and son.
"I support the departure of Dilma," he said. "The biggest corruption scandals occurred during her administration and she said nothing."
Dozens of political figures, including close allies of Rousseff, and former Petrobras executives are under investigation over a kickback and money laundering scheme that saw an estimated $3.8bn creamed off inflated contracts over a decade at the state-owned oil producer.
No one has yet been convicted, but some of the alleged wrongdoing took place while Rousseff was chairman of the Petrobras board.
Source: Al Jazeera and agencies