Partial results from Brazil's presidential election show left-wing candidate Luiz Inacio Lula da Silva has won nearly twice as many votes as his nearest opponent.

But it appears he will fall short of the absolute majority needed to be declared the winner after the first round of voting.

A head-to-head battle is now almost certain to take place on 27 October to decide if Mr da Silva, the former metalworker and trade union activist universally known as Lula, will become president.

Lula: Wants to lead his country to progress

His challenger is likely to be Jose Serra, the candidate backed by President Henrique Cardoso's centrist coalition, and correspondents say the outcome of the run-off is far from certain despite Mr da Silva's first-round lead.

With 90% of ballots counted, Mr da Silva had won about 47% of the vote, with Mr Serra trailing him on 24%.

Thousands of Lula supporters had gathered on Sao Paulo's main Paulista Avenue, waving red flags and hoping to celebrate an emphatic victory for their candidate.

But Lula campaign spokesman Andre Singer said the 56-year-old former union boss had expected a run-off and was "happy and confident" he would win it.

Run-off prospects

Mr da Silva has made it through to the second round before, only to fail to win the presidency, but he has not had such high levels of first-round support before.

Correspondents say the run-off will be closer, as Mr Serra will be able to concentrate solely on attacking Mr da Silva and his policies rather than worrying about the other two candidates who were vying for second place.

Few analysts are predicting that Mr da Silva will lose a second round, but none are prepared to rule it out either.

Government-backed candidate Jose Serra looks set for the run-off

The result of the presidential election is seen as crucial, as it is widely believed that it could dramatically change the political direction of Latin America's biggest country and have repercussions far beyond the region.

If Mr da Silva is victorious, he would become Brazil's first elected leftist leader.

But while a Lula victory may bring hope to the millions of Brazilians who live in poverty, the reaction of the financial markets will be crucial.

Brazil has seen its currency plunge amid investors' worries over Mr da Silva's ability to run the economy, and concern has grown that the country might default on its $260bn debt.

Mr da Silva has toned down his left-wing rhetoric, stressing that he would respect international agreements and stick to stable economic policies.

Before the poll, Mr Serra said he was convinced he could force a run-off and then pull together a strong enough anti-Lula coalition to claim the presidency for himself.

It seems he will get that chance as he is ahead of the other two candidates, former state governors Anthony Garotinho and Ciro Gomes.

All four candidates have campaigned on platforms of social change in a country beset by poverty, unemployment and wide income disparities.

Sunday's vote was also to elect the state governors, who wield considerable power, and senators and deputies to the federal congress where no party is likely to achieve a majority. State deputies were also chosen.