By Rodrigo Viga and Alonso Soto
RIO DE JANEIRO/BRASILIA (Reuters) - Tens of thousands of protestors poured onto the streets of major cities on Sunday to demand the removal of President Dilma Rousseff amid Brazil's worst political and economic crisis in a generation.
The demonstrations are the latest in a wave of anti-government rallies that lost momentum late last year but could gain strength as a sweeping corruption investigation nears Rousseff's inner circle.
The magnitude of the protests on Sunday could be decisive in convincing a divided Congress to back ongoing impeachment proceedings against Rousseff. The leftist leader is blamed by many in Brazil for sinking the economy into its worst recession in at least 25 years.
Polls show that more than half of Brazilians favor the impeachment of Rousseff, who was re-elected by a slim margin for a second four-year term in 2014.
Rousseff is the latest leftist leader in Latin America to face social upheaval as a decade-long commodities boom that fueled break-neck growth rates comes to an abrupt end.
Tensions ahead of the demonstrations were high after Sao Paulo state prosecutors requested the arrest of Rousseff's political mentor and predecessor, Luiz Inacio Lula da Silva, on money-laundering charges.
Rousseff has called for calm as her government fears clashes between pro- and anti-government protesters.
Demonstration were peaceful with thousands clad in the national yellow and green colors and holding banners that read "Dilma out" and "Stop with corruption."
"This government cannot stay in power any longer. This is not a class war between the poor and the rich, but a fight against corruption," said Andre Cerqueira, a civil engineer protesting on the ocean city of Rio de Janeiro.
In the capital Brasilia, protestors inflated a giant doll of Lula wearing a striped prison uniform and chained to a ball that read "Operation Carwash" - the name of the investigation centered on state oil company Petrobras. Police estimated about 50,000 protesters in the Brasilia alone.
Although no official nationwide figures were immediately available, authorities expect the demonstrations to be as big as the anti-government rallies of March 2015, which gathered as many as one million people.
A few hundred government supporters wearing red shirts and holding banners that read "There will not be a coup" stood outside the home of Lula in the outskirts of the city of Sao Paulo.
Popular discontent grew in recent weeks after a ruling party lawmaker reportedly used plea bargain testimony to accuse Rousseff and Lula of trying to hamper the Petrobras investigation. The probe has implicated senior politicians from Rousseff's coalition as well as top business executives.
The two-year-old probe has strained Rousseff's ties with her main coalition partner, Brazilian Democratic Movement Party (PMDB). At its national convention on Saturday, the PMDB threatened to break with her government and join the opposition.
Brazilian assets have rallied in recent weeks as investors bet that a change in government would lift business and consumer confidence and rescue an economy that contracted 3.8 percent last year.
Rousseff, whose popularity is near record lows, has said she will not quit and blamed her opponents for creating the crisis that is sinking an economy.
Political tensions have stalled Rousseff's legislative agenda that included measures to limit public spending and overhaul a costly pension system to regain the trust of investors.
(Editing by Daniel Flynn and Angus MacSwan)