Pro-government demonstrators took to the streets in several states amid fears of violence as the debate began. Major trade unions and landless peasant movements planned bigger, nationwide protests on Sunday, when the debate is set to culminate with a vote that Rousseff is widely expected to lose.

The government lost a last-ditch appeal on Thursday before the Supreme Court to halt the impeachment process, which could bring further instability or even chaos to Latin America`s largest economy after 13 years of rule by the leftist Workers` Party.

Rousseff is accused of manipulating budget accounts in 2014 to secure her re-election.

She has strongly rejected the accusation and planned to appeal to Brazilians in a televised speech on Friday night. But the increasingly isolated leader canceled the broadcast after an opposition party sought a court injunction to block it, arguing that she was unfairly using resources of the Brazilian state to defend herself.

Rousseff is fighting to survive a political storm fueled by Brazil`s worst recession since the Great Depression in the 1930s and a spiraling corruption scandal that has reached her inner circle.

In a further blow for the president, Minister for Cities Gilberto Kassab resigned his post late on Friday, according to two sources familiar with matter. His Brazil Social Democratic Party (PSD) split from the government on Wednesday and said it would vote for Rousseff`s impeachment.

Police stepped up security in the Brazilian capital where a half-mile-long (1 km) metal fence has been erected on the grass esplanade opposite Congress to avoid clashes between rival demonstrators expected to turn out by the tens of thousands over the weekend.

In Rio de Janeiro, police said they plan to form a cordon on the Copacabana beachfront avenue to separate the pro-impeachment crowd from Rousseff supporters.

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