Brazil's Supreme Court has rejected a last-ditch attempt by President Dilma Rousseff to avert an impeachment vote in congress, further reducing her chances of survival as a new poll showed her short of crucial support.
Rousseff's attorney-general, Jose Eduardo Cardozo, had asked the top court for an injunction to suspend Sunday's lower house vote until the full court can rule on what he called procedural flaws in the impeachment process.
But the court dismissed the motion 8-2 during a session that ran into the early hours.
Before the decision, a new survey by the Estado de S.Paulo newspaper showed for the first time that Rousseff's opponents had already secured the 342 lower house votes needed to advance impeachment.
Rousseff, an unpopular leader already struggling with Brazil's worst economic crisis in decades and a spiralling corruption scandal, has seen support from within her governing coalition steadily erode.
If her impeachment is approved by the required two-thirds majority of 513 house members, the senate must then vote on whether to go ahead with putting Rousseff on trial for breaking budget laws.
That could clear the way for Rousseff's suspension and replacement by Vice-President Michel Temer as soon as early May, pending a trial that could last six months.
Rousseff, a former leftist guerilla, had not been expected to resort to the Supreme Court until after Sunday's vote.
Cardozo's request to the court was seen as a sign, even before the latest newspaper survey, that her government now expects defeat.
Vowing to fight to the end, Rousseff met her political advisers as her government scrambled for votes to block impeachment, but defections by several centrist allies in her coalition have seriously compromised that effort.
Brazil's largest political party, the president's main coalition partner until it broke away two weeks ago, said most of its members in the lower house will back deposing her.
Leonardo Picciani, the lower chamber leader for the party, the Brazilian Democratic Movement Party, or PMDB, told reporters that 90 per cent of the 68 members of his caucus would vote for impeachment.
If Rousseff is ousted, it would end the 13-year rule of her leftist Workers' Party, which has lifted millions of Brazilians out of poverty and is overwhelmingly supported by the poor.