The presidential frontrunners are Luis Arce, who champions a return to the socialist and pro-indigenous policies of former president Evo Morales, and Carlos Mesa, a centrist who served as president in the early 2000s.

Polls show Arce ahead but not enough to avoid a run-off, which would take place in late November.

Several other centrist and conservative candidates are also on the ballot in Sunday's vote.

"The vote is set to be the most important since Bolivia returned to democracy in 1982," said Carlos Valverde, a political analyst.

The election will be a test of the left's clout in Latin America, as Morales was a key figure in a wave of leftist presidents in the region during the past decade.

Bolivia erupted in violence late last year when Morales sought a fourth term in a disputed election that has since been annulled. The violence cost at least 30 lives, sparked food shortages and forced Morales to resign after almost 14 years in power.

On Saturday, La Paz, a city starkly divided by class and race, appeared calm with little partisan activity. But residents across town acknowledged they are worried the result of Sunday's vote could spark more violence, especially if Arce's vote count falls short.

Arce told local media this week that the only way his rival could win is "through fraud".

The election was originally scheduled to take place in May but was postponed several times due to concerns about the coronavirus pandemic.

Australian Associated Press