Evo Morales speaks in a press conference in the city of El Alto, Bolivia, Nov. 10, 2019. (Xinhua)

International observers on Wednesday declared Bolivia's presidential election transparent and Luis Arce's incoming government legitimate as an official but not yet complete tally showed an overwhelming victory for the leftist.

"People voted freely and the result was clear and overwhelming, granting strong legitimacy to the incoming government, to Bolivian institutions and to the electoral process," Manuel Gonzalez, head of the observer mission for the Organization of American States (OAS), said in releasing the team's preliminary report on Sunday's polls in a video on Twitter.

With more than 90 percent of polling places accounted for, Arce has 54.51 percent - far more than needed for an outright victory for the 57-year-old economist from the Movement for Socialism (MAS) in the first round.

Centrist ex-president Carlos Mesa has 29.21 percent, followed by right-winger Luis Fernando Camacho with 14.19 percent.

The findings by the OAS are a sharp difference from 2019 elections, when Arce's former boss Evo Morales won a fourth term in polls that sparked weeks of protests, leaving 36 dead and 800 injured.

A later OAS audit found clear evidence of fraud.

"Thanks to the audit report carried out after last year's elections, today the country has an independent electoral authority and had a more equitable and transparent contest," said Gonzalez, a former Costa Rican foreign minister.

Despite this, hundreds of Bolivians have protested in Santa Cruz, a right-wing bastion, and in Cochabamba, claiming fraud in Arce's win.

In addition to the OAS findings, the results have been in line with projections from two private polling firms on the night of the election.

The European Union and US-based Carter Center also sent missions for the vote.

The Bolivian constitution declares the candidate who obtains an absolute majority or 40 percent of the vote with a 10-point advantage over their ­nearest challenger as the winner in the first round. Otherwise, there must be a ­second round.