Brazilians head to the polls Sunday in a closely watched presidential election between incumbent Luiz Inácio Lula da Silva and Sen. Flávio Bolsonaro.

The leading candidates are ideological opposites.

If no candidate secures more than 50% of the vote, the two top contenders will face each other in a runoff on Oct. 25 in Latin America’s largest economy. Ten other candidates are expected to receive far fewer votes.

Bolsonaro, 45, is the son of far-right former President Jair Bolsonaro and an ally of U.S. President Donald Trump. Lula, 80, is among the world’s oldest heads of state and is seeking the presidency for a seventh time. During his tenure, he has worked to strengthen Brazil’s ties with Beijing.