Luis Arce set to win Bolivia presidential election, returning socialists to power

Bolivia's socialists all but sealed a dramatic election comeback after their centrist rival Carlos Mesa conceded the vote on Monday, with several unofficial vote counts giving the Movement for Socialism party (MAS) of ousted leader Evo Morales an unassailable 20 percentage-point lead.

The win, still to be confirmed by the official count, would sweep the party of leftist Morales back into power a year after he was forced to resign following a fraught election that sparked widespread protests and violence.

The socialist MAS party's candidate Luis Arce, 57, took more than 50 per cent of the votes, rapid counts showed, and Mesa with about 30 per cent, a far larger gap than pollsters had predicted.

"The result of the quick count is very strong and very clear," Mesa said at a news conference after the socialist party had claimed victory in the early hours of the morning, despite the official count still in its early stages.

"The difference between the first candidate and the Comunidad Ciudadana (Civic Community) is wide and it is up to us, those of us who believe in democracy, to recognize that there has been a winner in this election."

Arce's team on Monday said that the initial results looked "hard to change" but that the former finance minister during Morales's near-14 year socialist administration would only make a statement once the official results were complete.

That process may take several days. The official count on Monday afternoon had tallied around a quarter of the votes, showing Mesa slightly ahead but widely expected to gradually fall back as more votes were counted from MAS strongholds.

"All the data known so far indicates that there has been a victory for the Movement for Socialism," Morales, who handpicked Arce and has been closely advising the campaign, said in a news conference in Buenos Aires late Sunday night as the initial returns came in.

Arce is a former economy minister under Morales.

Body blow to conservatives

The result is a body blow for Bolivia's conservatives, who had hoped to present a new model for the country beyond Morales, who sought an unprecedented fourth term last year despite term limits, which had led to protests again him.

Arce, a close Morales ally, may bring a more moderate and technocratic stance than his former boss, who oversaw stable growth and elevated Indigenous groups but drew criticism for an authoritarian streak and trying to hold on too long to power.

"This could be the beginning of a new era for the MAS party, replacing Evo," said Franklin Pareja, a political analyst.

The win could also see Morales return from exile in Argentina, where he has been living since fleeing the country after his resignation last year when he claimed there had been a right-wing coup against him.

Morales in a news conference on Monday indicated he intended to go back to Bolivia, though Arce has cautioned he would have to deal with outstanding Justice department investigations before returning to a government role.

Morales had been one of the longest-standing leaders of Latin America's so-called pink wave of left-wing governments, who won plaudits for his support of Indigenous groups.

Arce, a trained economist who studied at the University of Warwick in England, drew support from leftists around the region, including in Mexico, Argentina, Cuba and Venezuela.

"We celebrate that a serious conflict was resolved by peaceful and democratic means," tweeted Mexican president Andrés Manuel López Obrador.