Troop reinforcements have been drafted into Rio de Janeiro as Brazil prepares to hold nationwide elections for president, state governors and Congress.

The authorities, who have 30,000 troops and police at their disposal, have decided to mount a show of force amid fears that drugs gangs operating out of Rio's sprawling favelas or shanty towns could try to disrupt the voting.

Lula: Confident of victory but will he win the first round outright?

Ahead of the ballot, officials have been conducting last-minute checks on a computerised voting system being used across the country for the first time in a presidential election.

Leftist Workers Party presidential candidate Luiz Inacio Lula da Silva has a massive lead in the opinion polls and will be hoping to win the absolute majority needed to avoid a second round of voting in Latin America's economic power-house.

Independent surveys suggest that success for Mr da Silva, who is universally known as Lula, could hang on the votes of just 1% of Brazil's 115 million electorate.

But Lula has stressed that he is not guaranteed victory.

Brazil votes

115.2m voters Voting compulsory for over-18s 406,000 computer ballot boxes Polls open 1100 GMT, close 2000 GMT

"I'm not going to thank you yet because this race is not over," he said.

"We don't know if we're going to a second round and if we do, we're going to have to start a second phase of the campaign on Monday."

His most likely opponent if it goes to a run-off on 27 October is Jose Serra, the candidate backed by outgoing President Fernando Henrique Cardoso.

The other two candidates are former state governors Anthony Garotinho and Ciro Gomes.

Fears

The election is being played out amid intense uncertainty in the financial markets.

The prospect of a Lula victory has already prompted investors to pull money out of the country and caused a big slump in the currency.

Investors are worried Lula will be unable to manage Brazil's economy

The former union boss has toned down his left-wing rhetoric, stressing that he would respect international agreements and stick to stable economic policies.

As well as the economy, another major election issue has been crime and violence, a reflection of the social problems in a country with huge disparities between rich and poor.