BRASÍLIA, Brazil |(AFP) – Brazilian lawmakers were set to vote shortly Sunday on impeachment of President Dilma Rousseff in a tension-filled showdown watched by millions around the deeply divided Latin American powerhouse.

Months of rancorous debate that have seen Rousseff’s ruling coalition collapse and prompted huge street demonstrations were coming to a head in the capital Brasilia where the lower house of Congress was to vote on authorizing an impeachment trial.

Latest estimates in major Brazilian newspapers were that pro-impeachment deputies in the house would succeed. They need 342 of the 513 votes, or two thirds of the house.

But Jose Guimaraes, a senior member of Rousseff’s Workers’ Party, said he remained optimistic in “the final stretch of a decisive battle.”

“Our latest estimate is that we have enough votes to defeat impeachment,” he told journalists. “The opposition is far from 342.”

Party leaders were to make final arguments at about 1700 GMT before voting starts. The whole procedure was to be aired live on television to the country of 204 million, the biggest in Latin America, and also on screens erected in city squares.

Demonstrators for and against Rousseff took to the streets ahead of the vote under the eye of riot police.

In Brasilia, a huge metal barrier was raised to separate rival protesters and in Rio de Janeiro, which is scrambling to organize the Olympics this August, the two sides were demonstrating at separate time slots on Copacabana beach.

So far, the atmosphere on the streets was peaceful, even festive, with a funk band singing in Rio and protesters blowing trumpets and vuvuzuelas, as if at a football game, in Brasilia.