Brazilian voters began casting ballots on Sunday in a high-stakes presidential contest between President Luiz Inácio Lula da Silva and Flávio Bolsonaro, the son of former president Jair Bolsonaro.

The Associated Press reported that almost 159 million people are eligible to vote. If no candidate wins more than half of the valid votes, a runoff is scheduled for 25 October. Brazilians are also choosing governors and members of Congress, making the election a test of the country’s executive and legislative balance as well as its presidency.

Flávio Bolsonaro has positioned himself as an ally of US President Donald Trump. That alignment has made the election part of a wider argument about Brazil’s place in the Americas and about the influence of Washington on the country’s politics. Lula, meanwhile, has maintained close ties with Beijing, adding a foreign-policy dimension to a contest already shaped by domestic polarisation.

The voting system itself is electronic, and the credibility of the result will depend not only on the count but on whether the competing camps accept the institutions overseeing it. Brazil’s electoral authorities have long experience administering national votes, but the intensity of the contest means that claims made before and after polling will be closely watched.

The stakes are wider than the identity of the next president. Brazil is Latin America’s largest economy, a major agricultural exporter and a significant diplomatic actor in the Global South. Its choices affect trade, climate diplomacy, relations with China and the balance of power in the region.

The first-round vote will not settle every dispute. It will establish the strength of each political coalition and show whether voters prefer Lula’s incumbent administration or a Bolsonaro-led return to the political line associated with the former president. The runoff, if required, will decide which of those projects governs Brazil.