Bolivia is heading for a runoff presidential election with centrist Senator Rodrigo Paz and right-wing former President Jorge "Tuto" Quiroga set to face each other following a result that surprised pre-vote polls.

With 90 percent of the ballots from Sunday's vote tallied, the National Electoral Council (CNE) announced that Paz had secured 31 percent of the vote while Quiroga came in second with 27 percent.

Paz, a 57-year-old from the Christian Democratic Party, is a surprise frontrunner. 

He is the son of former President Jaime Paz Zamora, who ruled from 1989-1993. 

Born in Spain during his family's exile from 1964 to 1982, Paz's political career began as a lawmaker in 2002. He later served as mayor and governor of his native Tarija region. 

Paz gained modest notoriety as the campaign progressed.

Jorge “Tuto” Quiroga, 65, of the Alianza Libre coalition, is the second contender in the run-off. 

Quiroga, who has run for president unsuccessfully three times before, previously served as president from 2001 to 2002. 

He completed the final year of former military dictator Hugo Banzer's term after Banzer resigned due to lung cancer.

​​“Bolivia told the world that we want to live in a free nation. It's a historic night,” Quiroga said at a public event after the preliminary results were announced.

The polls had widely predicted that Samuel Doria Medina, a 66-year-old center-right businessman, would compete against Quiroga in the second round. 

However, Medina, who has made three failed presidential bids, came in third. 

The five other candidates in the race, including leftist Andronico Rodriguez, trailed far behind.

Both candidates leading the race have promised to distance themselves from the state-led economic model imposed by the ruling Movement for Socialism (MAS) party. 

This model, some Bolivians argue, is the cause of the country’s current economic crisis, which is characterised by a shortage of US dollars, a steady rise in living costs, and prolonged periods of fuel scarcity due to a reliance on imports.

A run-off, widely anticipated because no single candidate won the required majority in the first round, is scheduled for October 19. 

To win the first round, a candidate needed either more than 50 percent of the vote or at least 40 percent with a 10-point lead over the runner-up.

In addition to the president and vice president, voters also voted for 36 senators and 130 deputies.

A vote for change 

Gustavo Flores-Macias, a political scientist at Cornell University in the United States, said Paz's late surge showed people were "tired of the same candidates" repeatedly running for the top job.

Flores-Macias also linked Paz's success to a widespread disdain in Bolivia for candidates with links to big business.

The vote brings the curtain down on 20 years of socialist rule, which began in 2005 when Evo Morales, an Indigenous coca farmer, was elected president on a radical anti-capitalist platform.

Bolivia enjoyed more than a decade of strong growth and Indigenous upliftment under Morales, who led the country from 2006 to 2019.

But underinvestment in exploration caused gas revenues - the country's main earner - to implode, eroding the government's foreign currency reserves and leading to shortages of imported fuel and other basics.

"The left has done us a lot of harm. I want change for the country," Miriam Escobar, a 60-year-old pensioner, told AFP after voting in La Paz.