President of the Brazilian Senate Renan Calheiros (R) listens to Senator Aecio Neves during a ssession debating on the voting of the impeachment of President Dilma Rousseff in Brasilia, Brazil, May 11, 2016. [Photo/Agencies]

BRASILIA - The Supreme Court rebuffed a last-ditch bid by President Dilma Rousseff to halt a vote in the Senate on Wednesday that is expected to put her on trial for breaking budget laws and end 13 years of leftist rule in Latin America's biggest country.

If her opponents garner a simple majority in the 81-seat Senate in a session that will last late into the evening, Rousseff will be replaced on Thursday by Vice President Michel Temer as acting president for up to six months during the trial.

There were signs Rousseff was preparing for defeat: she plans to dismiss all her cabinet and has given instructions that there should be no easy transition for a Temer government because she considers her impeachment illegal, presidential aides said.

With a change of government imminent, Temer plans to swear in new ministers on Thursday afternoon, Senator Romero Jucá, head of his Brazilian Democratic Movement Party (PMDB), told reporters.

Rousseff, who has been in office since 2011, has seen her popularity crushed by Brazil's worst recession since the 1930s and a two-year probe into a vast kickback scheme at state-run oil company Petrobras.

The prospect of business-friendly Temer taking power has driven Brazilian financial markets sharply higher this year, on hopes he could cut a massive fiscal deficit, restore investor confidence and return the economy to growth.

The political crisis has deepened Brazil's recession and comes at a time when Brazil hoped to be shining on the world stage as it prepares to host the Olympic Games in Rio de Janeiroin August.

A Supreme Court judge denied an injunction Rousseff sought on Tuesday to halt the Senate vote. Justice Teori Zavascki rejected as "legally implausible" the government's argument that impeachment was flawed because it was started out of revenge by the former speaker of the lower house.

In a momentous session followed by many Brazilians live on television, each senator was given the chance to speak. A final vote could take place after midnight (0300 GMT on Thursday).