Bolivia's election observer will convene a special meeting on Wednesday after a disputed presidential vote showed President Evo Morales would win outright, which sparked angry protests around the South American nation.

The Organization of American States (OAS), an official observer of the election, raised concerns after an official rapid count of votes gave Morales, a leftist in power since 2006, a 10-point lead over rival Carlos Mesa. This result, which would allow Morales to avoid a risky second round, came after a preliminary count was abruptly halted following the vote on Sunday. With nearly 84% of ballots counted, Morales and Mesa appeared to be heading for a run-off.

A binding vote-count is still underway and could take days to finish.

The OAS raised concerns about the "hard-to-explain" change in the overall trend of the result, which it said "drastically modified the fate of the election and generates a loss of confidence in the electoral process."

On Tuesday, pockets of protesters remained on streets around the country after a night of rioting and skirmishes between voters and police, which saw a number of vote counting stations and ballot boxes set ablaze.

In one case, in the city of Potosi, two people jumped from a burning building to escape the flames.

In downtown La Paz on Tuesday, roads and markets were clogged with residents loading up with rice, cooking oil, potatoes and other basics.

A political group affiliated with Morales, Conalcam, slammed the unrest, saying it was orchestrated by the right-wing opposition. The group called on supporters to defend Morales' "victory" with peaceful counter-protests.

The preliminary count from the Supreme Electoral Tribunal (TSE) said Morales had 46.85% of the vote to Mesa's 36.74%, just giving him the 10-point lead needed.

Mesa said he did not recognize the result, while the OAS said it would recommend a second-round.

"This is a tragic day for Bolivian democracy," Carlos Alarcon, a representative of Mesa's Citizen Community party, said at a protest site late on Monday.

Morales "has once again robbed the vote, the right to decide by our votes who will be president of Bolivia."

Morales has kept a low profile since confidently claiming on Sunday night that the eventual vote would hand him an outright victory.

MASKED YOUTHS, TEAR GAS

Videos broadcast on social media and TV showed protesters pulling down a statue of late Venezuelan President Hugo Chavez in the city of Riberalta, and pitched battles between police and masked youths amid plumes of tear gas.

As fears of a prolonged turmoil spread, long lines formed at some gas stations and supermarkets. Local food and energy associations put out statements that there was no shortage of supplies.

The unrest marked a major jolt for the land-locked country, which has had a long stretch of political stability under Morales, Bolivia's first indigenous president and South America's longest continuous-serving standing leader.

Morales has not made any public appearances since declaring victory late on Sunday. Early on Tuesday, he took to Twitter to remind Bolivians of high rates of poverty under a right-wing government in the 1990s.

Late on Monday, Morales' interior minister, Carlos Romero, warned Mesa and his supporters not to stoke violence. "If someone goes too far and doesn't measure the consequences, that's their responsibility," Romero said.