Sebastian Pinera is a wealthy conservative businessmen who was previously Chile's president between 2010 and 2014. Photo: AFP

A billionaire looking to regain the presidency and a former TV presenter were Sunday competing in an election run-off to lead Chile, with the outcome far from certain.

The South American country's 14 million voters were being called to cast ballots at more than 43,000 polling stations across the country. Voting opened at 8:00 am local time (1100 GMT) and was due to close at 6:00 pm (2100 GMT), with results given soon afterward.

Sebastian Pinera, a wealthy conservative businessmen who was already president between 2010 and 2014, is seeking a to succeed outgoing President Michelle Bachelet, who steps down in March next year and cannot try for re-election.

He had been seen as the favorite -- until the first round held on November 19 revealed surprisingly strong support for the left.

That surge could coalesce behind Alejandro Guillier, a senator and former TV presenter who is independent but supported by Bachelet.

In the first round, Pinera garnered a lower-than-expected 37 percent of the vote to Guillier's 22 percent.

Guillier could pick up much of the 20 percent that went to anti-austerity radical-left candidate, Beatriz Sanchez, who was knocked out of the race.

Analysts said a high turnout would likely benefit Guillier.

- Candidates confident -

Chile's 14 million voters were Sunday being called to cast ballots at more than 43,000 polling stations across the country. Photo: AFP

Voting took place under a somber cloud following the deaths of five people and the disappearance of 18 more in a mudslide in the country's south.

Bachelet urged citizens to take part as she cast her ballot.

"In a democracy, one has to respond by also making one's voice heard through voting," she told journalists.

The two candidates projected confidence as they voted in their respective polling stations.

"I have the firm conviction that we are going to win these elections and that better times are going to come for all Chilean households," Pinera said.

Guillier, speaking in the northern town of Antofagasta, said he expected he would seize a "close but clear" victory.

One analyst, Marcello Mella at the University of Santiago, said before the run-off that the election "will probably come down to a difference of less than 20,000 votes."

- Slow growth -

Alejandro Guillier, could pick up much of the 20 percent that went to anti-austerity radical-left candidate in Chile's first round vote. Photo: AFP

Though copper exports, which contribute greatly to Chile's wealth, are increasing thanks to demand from China and from the burgeoning manufacture of electric cars, the country is struggling relative to previous years.

Its GDP is forecast to expand a modest 1.4 percent this year, the slowest pace in eight years.

Pinera, 68, and Guillier, 64, are also promising to expand free university tuition brought in under Bachelet -- a measure with historical resonance in Chile because paid tuition was introduced under the 1973-1990 military dictatorship of Augusto Pinochet.

For Pinera, the vow was a U-turn, contradicting an earlier statement he made that "free things mean less commitment."

Bachelet's exit will be her second as president. She became the country's first female head of state in 2006. Pinera took over in 2010. Then Bachelet returned in 2014.

Whoever wins Sunday's election will take office from March 2018 until 2022.