Dilma Rousseff, the leading candidate for Brazil's next presidency, will head to a runoff later this month after failing to win enough votes to become the country's first female president.

With 98 per cent of the votes counted in Sunday's poll, the supreme electoral court said Rousseff captured 46.6 per cent of the vote, former Sao Paulo state governor Jose Serra got 32.8 per cent support, and Green Party candidate Marina Silva received 19.5 per cent.  

Rousseff needed 50 per cent-plus-one to avoid a knockout round against Serra, and will have to face Serra in the runoff on October 31.

Al Jazeera's Lucia Newman reports from the Brazilian city of Sao Paulo.