Demonstrators cheer in Sao Paolo on Sunday while watching a big screen that shows congressional actions authorizing impeachment proceedings against President Dilma Rousseff. [Photo/Agencies]

Brazil awoke on Monday to deep political crisis after lawmakers authorized impeachment proceedings against President Dilma Rousseff, sparking claims by supporters that democracy was under threat in Latin America's biggest country.

Opposition deputies in the lower house of Congress needed 342 of the 513 votes, or a two-thirds majority, to send Rousseff's case to the Senate, which will now decide whether to open a trial. They reached that number near midnight on Sunday, after five hours of voting.

Wild cheering and a burst of confetti erupted from opposition ranks at the 342nd vote, countered by furious jeering from Rousseff allies in a snapshot of the bitter mood consuming Brazil just four months before Rio de Janeiro hosts the Olympics.

Jacques Wagner, the president's chief of staff, accused deputies of voting for impeachment without proving that the leftist president, who is accused of illegally manipulating budget figures, had committed a serious crime.

"In this way, the Chamber of Deputies is threatening to interrupt 30 years of democracy in the country," he said, referring to the end of a military dictatorship in 1985.

"It was a coup against democracy," said Rousseff's attorney general, Jose Eduardo Cardozo.

Cardozo said that Rousseff — who was imprisoned and tortured under military rule in the 1970s — would give her first public reaction on Monday.

There was expected to be a euphoric reaction from the financial markets, which have been betting heavily on a Rousseff exit and the advent of a more business-friendly government to kick-start Brazil's flailing economy.

Outside Congress, where tens of thousands of people were watching giant TV screens, the split was echoed on a massive scale — with opposition supporters partying and Rousseff loyalists in despair.

"I am happy, happy, happy. I spent a year demonstrating in hope that Dilma would be brought down," said retiree Maristela de Melo, 63.

Rousseff supporter Mariana Santos, 23, burst into tears, saying the vote was "a disgrace for our country".

Several thousand police officers stood by, and the rival camps were separated by a long metal wall.

Rousseff, 68, is accused of illegal accounting maneuvers to mask government shortfalls during her 2014 re-election. Many Brazilians also hold her responsible for the economic mess and a massive corruption scandal centered on state oil company Petrobras — a toxic record that has left her government with a 10 percent approval rating.

Now the decision by the lower house moves the matter to the Senate, which is expected to vote in May on whether to open a trial. If a trial were approved — which experts consider almost certain — Rousseff would step down for up to 180 days while the trial got underway.

If the Senate then voted by a two-thirds majority for impeachment, Rousseff would be ousted and Vice-President Michel Temer would take over until elections in 2018.