The winner will take office in January to replace corruption-tainted Jimmy Morales, who leaves with his popularity at rock bottom.
Polling stations open at 8 am (0600 GMT) and close at 8 pm, followed immediately by two exit polls. The focus will be on challenges in the Nordic country's welfare model and on two new far-right anti-immigrant parties.
Electoral commission says President Peter Mutharika, who is fighting for a second five-year term in office, has 40.49 percent of the vote.
The riots came after the General Election Commission announced President Joko Widodo had beaten his challenger former general Prabowo Subianto in the April 17 presidential poll.
Invalid counting sheets, not deploying civil servants at polling centres are the main reasons cited for a revote of March polls.
The vote is seen as the toughest test yet for the governing African National Congress (ANC) party, 25 years after it swept to power at the end of white minority rule.
North Macedonia's pro-Western candidate, Stevo Pendarovski, won a run-off presidential vote after a campaign dominated by divisions over a change to the country's name that was agreed to mollify Greece and open the way for EU and NATO membership.
Meet the candidates running for prime minister: Pedro Sanchez, Pablo Casado, Albert Rivera, Pablo Iglesias and Santiago Abascal.
Polls have opened and Ukrainians are voting in the second round of the country's presidential election. Here are five facts about a country at war wanting transformational change.
Dismayed by endemic corruption and a struggling economy, Ukrainian voters appear poised to strongly rebuke incumbent Petro Poroshenko and replace him with TV star Volodymyr Zelenskiy.
Indonesia's incumbent leader Joko Widodo faces off against ex-military general Prabowo Subianto in an election for president of the world's third-biggest democracy. The 2019 election is a re-run of the 2014 contest narrowly won by Widodo.
The election will pit Bill Shorten, a former labour union leader who has presented himself as the alternative prime minister for the past six years, and PM Scott Morrison, a leader who the Australian public is still getting to know.
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