Presidential candidate Evo Morales waves to supporters after voting during general elections at Villa 14 de Septiembre, some 170 km from Cochabamba, Bolivia. (AP Photo/Jorge Saenz)

A leftist candidate appears set to win an election and become Bolivia's first indigenous president, after his main rival conceded defeat amid reports that he was trailing far behind.

Evo Morales, a former coca farmer and union leader, has raised hackles in Washington with promises to fully legalize coca leaf production and nationalize the country's oil and gas industry.

Unofficial results tabulated by four local television stations gave between 47 per cent and 50 per cent of the votes in Sunday's election to Morales, who heads the Movimiento al Socialismo (Movement Toward Socialism or MAS) party.

Two independent surveys released after polling stations closed also indicated that Morales held the lead, with between 44 per cent and 45 per cent of the ballots.

His closest contender, conservative Jorge Quiroga, appeared to be trailing at between 33 per cent and 34 per cent, according to the exit polls.

Morales, 46, thanked a crowd of supporters in Cochabamba for his "great triumph," while warning them to wait for the official results.

"I am very content, very emotional about this," he said.

Quiroga conceded defeat Sunday night.

"I congratulate the candidates of MAS that have carried out a good campaign," said Quiroga, a former president who has strong support in areas that are rich in oil and gas production.

Morales support higher than expected

Morales appears to have won much more support than pre-election polls had predicted.

If he captures more than half the votes, he will be able to declare an outright victory. Otherwise, he will have to wait for the country's legislators to declare a winner in January.

Bolivians, who live in South America's poorest country, were also voting to choose a new parliament and regional governors.

Pledge to legalize coca worries U.S.

Morales, an Aymara Indian, has alarmed Washington with his pledge to fully legalize the production of coca.

Coca has traditionally been used by the country's indigenous population, including as tea.

However, it's also used to make cocaine and Bolivia is the third biggest producer of the drug, after Colombia and Peru.

Morales has never said he plans to legalize cocaine, but that hasn't reassured U.S. politicians who regard him as an enemy in their anti-drug campaign.

He's also antagonized Washington by flaunting ties to Venezuela's outspoken leftist President Hugo Chavez and Cuba's Fidel Castro.

"If [the U.S.] wants relations, welcome," said Morales, who waved a coca branch as he went to vote on Sunday. "But no to a relationship of submission."

Morales appeals to disenfranchised native population

Morales' promise to nationalize Bolivia's energy industry has raised alarm among the wealthy, largely white elite in Bolivia.

But it has won him widespread support in a country where about half the population of 8.5 million people is considered to live in extreme poverty.

Even though two-thirds of the population is indigenous, Morales is the first native leader to come within striking distance of the presidency.

Many of the country's natives feel the free-market economic policies of recent years have enriched the white elite at their expense.

Quiroga poses a stark contrast

His closest political rival couldn't be more different. A fair-skinned engineer educated in the United States who has already served in a previous government, Quiroga is pushing for closer ties with the United States and inviting more foreign investment.

Quiroga, who served as president from 2001 to 2002 after then-president Hugo Banzer became sick, has promised to continue a hard-line stand against coca production.

Bolivia has seen five presidents in four years, with street protests forcing out two presidents in the past two years.

Eduardo Rodriguez has acted as caretaker president since largely indigenous street protests ousted Carlos Mesa after only 18 months in office.