Brazil's senators are debating whether to put President Dilma Rousseff on trial over allegations that she illegally manipulated the budget to hide a growing fiscal deficit.
The debate, which continued into the early hours of Thursday, will be followed by a vote that could suspend Rousseff, the first woman to become Brazilian president, for the duration of the investigation, which would be 180 days.
After 18 hours of debate, in which each senator were given the opportunity to give a 15-minute speech, a majority had said Rousseff should face an impeachment trial.
Al Jazeera's Latin America Editor Lucia Newman, reporting from Brasilia, said Rousseff was expected to lose by an overwhelming majority.
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"It is a dramatic time for Brazil," she said. "Even the pope has weighed in, calling for prayers and dialogue."
Outside Congress, where a metal fence was erected to keep apart rival protests, about 6,000 backers of impeachment chanted "Out with Dilma" while police used pepper spray to disperse gangs of Rousseff supporters, who hurled flares back. One person was arrested for inciting violence.
If Rousseff's opponents garner a simple majority in the 81-seat Senate session, Rousseff will be replaced on Thursday by Vice President Michel Temer as acting president for up to six months.
On Wednesday, Brazil's Supreme Court rejected an appeal to block the Senate vote.
In April, the lower house of parliament voted to impeach Rousseff, who has been president since 2011.
But on Monday, Waldir Maranhao, the interim head of the legislature's lower house, threw the impeachment effort into disarray by annulling that vote, citing procedural problems.
He then reversed the decision several hours later, setting the stage for the vote in the Senate.
Deeply unpopular, Rousseff's presidency has been damaged by corruption scandals, political paralysis and a sharp economic downturn.
About 11 million people are out of work.
Rousseff faces impeachment over accusations of tampering with figures to disguise the size of Brazil's budget deficit during her 2014 re-election campaign.
She has denied any wrongdoing, and cast the efforts to remove her as a coup.
Source: Al Jazeera and agencies