The impeachment process against Brazilian President Dilma Rousseff was abruptly halted after the leader of Brazil's Lower House agreed to annul last month's vote by legislators to put her on trial.

The surprise announcement came just ahead of an impeachment vote in Brazil's Senate on Thursday that was likely to suspend Rousseff from office.

Congressman Waldir Maranhão, the interim speaker of Brazil's chamber of deputies, said in a statement that he decided to accept a request by Attorney-General José Cardozo to annul the April 17 vote to put Rousseff on trial, citing procedural irregularities. Maranhão said MPs should not have announced their votes in advance, and should not have been told how to vote by party leaders.

"For these reasons I annulled the session....and decided that a new session should take place," Maranhão said, adding that he'd asked the president of Brazil's Senate to return the impeachment measure to the Lower House for a new vote. He did not set a date, but said the vote would take place within five legislative sessions.

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But the head of the Senate, Renan Calheiros, said he had rejected the decision and that a vote in the Upper House on whether to put Rousseff on trial would continue as scheduled.

Maranhão's move seemed to whipsaw the entire country, including Rousseff.

In a speech today, she too seemed confused about the meaning of the decision. "I don't know the consequences," she said to a cheering crowd of supporters. "We have to find out what's happening."

Maranhão became acting Speaker of the House last week after Eduardo Cunha, the elected Speaker, was suspended by Brazil's Supreme Court. Cunha is accused of corruption by the same court.

About 70 per cent of Brazilian deputies voted last month against Rousseff, so dozens of legislators would have to change their minds about her impeachment in order for a future vote to break her in her favour.

That seems unlikely, so Maranhão's decision may only end up stalling Rousseff's impeachment, and would do little to bring stability to her Government.

"Brazil is in political intensive care, at the peak of an ethical and institutional crisis," said Claudio Lamachia, president of the Brazilian Bar Association.

"The Brazilian Bar Association is very worried about the decision taken by the interim Speaker of the House," he said.

"This sort of action appeases the momentary interests of some political groups, but ignores the legitimate decisions already taken."