SAO PAULO -- Brazilians ratcheted up the heat for embattled President Dilma Rousseff on Sunday, turning out by the tens of thousands for demonstrations across the country calling for her ouster.
The biggest protest took place in Brazil's economic capital, Sao Paulo, a bastion of simmering dissatisfaction with Rousseff and her governing Workers' Party. The respected Datafolha polling agency estimated about 500,000 people took part in the Sao Paulo demonstration, while police estimates put turnout at nearly three times that number.
Organizers said about 1 million people joined the anti-Rousseff demonstration in Rio de Janeiro.
In a statement, Rousseff said, "The peaceful character of this Sunday's demonstrations shows 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."
The street rallies came two days after she rejected the idea of resigning.
The demonstrations add to an already-difficult position of Rousseff. She faces the twin problems of an impeachment effort in congress over alleged fiscal mismanagement amid the worst recession in decades and the sprawling investigation by federal prosecutors into corruption at state-run oil giant Petrobras that has moved closer to her inner circle in recent weeks.
Analysts said the strong turnout at the protests could further hamper Rousseff's ability to fight for her political survival and could lead to the unraveling of her fragile governing coalition.
"There is a situation of ungovernability," said Francisco Fonseca, a political science professor at Pontifical Catholic University in Sao Paulo. "The president has few cards."
Fonseca pointed out that the demonstrations continued to be dominated by the largely white, upper middle class demographic that has been staging regular protests against Rousseff for over a year.
"The poor who are affected by the economic crisis aren't in the streets," he said, adding Sunday's protests demonstrated a "generalized discontent with the political system" without necessarily shoring up any particular opposition party or politician.
Organized largely through social media, demonstrations took place in some 200 cities and towns across Brazil. Rousseff had raised fears of possible clashes between supporters of her party and the anti-government demonstrators, but no serious incidents were reported during Sunday's protests, which had a festive atmosphere.
Crowds in the yellow and green hues of the Brazilian flag brandished signs reading "Workers' Party out."
"She (Rousseff) has to go," said Patricio Gonzaga, an unemployed metal worker who took part in the Sao Paulo gathering. "She is the person responsible for the mess our economy is in - the inflation, recession and unemployment. She is to blame for me being unemployed and having trouble supporting my family."
Demonstrators across the country stressed that their anger extended well beyond Rousseff and the Workers' Party, saying the "Car Wash" investigation into corruption at Petrobras had compromised the entire political class.
"Of course I want to see Rousseff booted out," said Maria de Lima Pimenta, a retired schoolteacher who was at the anti-Rousseff march along Rio's Copacabana Beach. "But then the problem becomes, who will replace her? They're all crooks."
Protest organizers stressed that the movement isn't linked to any opposition political party, and signs endorsing parties were largely absent from the demonstrations.
But several top politicians turned out, including Aecio Neves, the opposition politician who narrowly lost to Rousseff in the 2013 presidential run-off election, and Sao Paulo state Gov. Geraldo Alckmin. Both were booed, and like other politicians who ventured out to the demonstrations, both beat a rapid retreat.
The Petrobras scandal has ensnared key figures from Rousseff's party, including her predecessor and mentor, former President Luiz Inacio Lula da Silva, as well as members of opposition parties.
Political tensions in Brazil have spiked since earlier this month when Silva was briefly detained by police for questioning as part of the Petrobras probe. Silva's supporters and detractors scuffled in front of his apartment in the Sao Paulo area.
On Wednesday, the tension rose again when Silva was hit with money-laundering charges in a separate case.
News reports have said Rousseff, whose second term runs through the end of 2018, has offered Silva a ministerial post that would shield him from possible imprisonment on any charges. Under Brazilian law, only the Supreme Court can authorize the investigation, imprisonment and trial of Cabinet members.
Rousseff said at a Friday news conference that she would be "extremely proud" to have Silva, a once-wildly popular leader who governed Brazil in 2003-2011, but declined to say whether he would join the government.
Turning to calls for her to quit, she said it was objectionable to demand the resignation of an elected president without concrete evidence the leader had violated the constitution.
"If there is no reason to do so, I will not step down," Rousseff said, calling on journalists at the event in Brasilia to "at least attest that I don't look like someone who is going to step down."