Brazilian President Dilma Rousseff attends a rally in Porto Alegre, Rio Grande do Sul on the eve of the general elections on Sunday.

AFP/Santiago

After a topsy-turvy campaign, Brazil votes in presidential elections on Sunday, with incumbent Dilma Rousseff headed for a likely runoff against one of two challengers promising very different brands of change.

The telenovela-like drama of the race - a candidate's death in a fiery plane crash, a poor maid's rise to the cusp of the presidency, a seedy oil scandal - continued down to the wire.

On the eve of the vote, Marina Silva, the environmentalist whose meteoric rise once looked unstoppable, slipped to third place behind business-world favourite Aecio Neves.

Three polls released on Saturday gave Silva, a one-time maid and rubber-tapper who has vowed to be multiracial Brazil's first "poor, black president," between 21% and 24% of the vote, trailing Neves (24-27%) and Rousseff (41-46%).

But the race for the second spot in a likely October 26 runoff was too close to call, with the gap between Neves and Silva less than the two-percentage-point margin of error in all three polls.

Either candidate would face an uphill battle to unseat Rousseff, Brazil's first woman president, who led the probable second-round race by a more than five-point margin against both.

The election, the closest in a generation for Latin America's largest democracy, is widely seen as a referendum on 12 years of government by Rousseff's Workers' Party (PT).

The sprawling country is divided between voters loyal to the PT for launching landmark social programs while presiding over an economic boom in the 2000s and those calling for an end to the corruption scandals, poor public services and four years of disappointing growth tainting Rousseff.

PT social programs have helped 40mn Brazilians escape poverty in the past 12 years.

But Rousseff, 66, has presided over an economic slowdown and, as of January, a recession, as well as protests last year against corruption and widely disdained public education, healthcare and transport.

Rousseff, a former guerrilla who was jailed and tortured for fighting the country's 1964-1985 dictatorship, has also been battered in recent weeks by a corruption scandal implicating dozens of politicians - mainly her allies - at state-owned oil giant Petrobras.

The campaign was upended on August 13 when then-third-place-candidate Eduardo Campos of the Socialist Party died in a plane crash.

Silva, his 56-year-old running mate, swooped into the race with a promise to bring a "new politics" to Brazil.

A well-known environmentalist and member of the country's surging Evangelical Christian community, she drew support from both religious conservatives and the left and was initially projected to beat Rousseff in a runoff.

Neves, 54, a former governor from the powerful Social Democratic Party (PSDB) with a reputation as a playboy, meanwhile faded into a distant third place.

Some 142.8mn voters will cast their ballots in the polls. First results are expected late in the evening.

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