An attempt by Bolivian President Evo Morales to run for another term by amending the constitution appeared to be heading towards a slim electoral defeat, according to unofficial partial vote counts and early results.

Morales, 56, now serving a third term, was trying to change the constitution so that he could run for re-election in 2019, potentially allowing the former coca grower to remain president until 2025.

But exit polls showed that he may have lost the vote. An Ipsos poll had the "no" side at 52.3 percent and "yes" at 47.7 percent, while a Mori poll gave a narrower 51 percent to 49 percent lead to the "no" side.

Early official results had the "no" side winning with 66 percent of votes, although that covered only 3 percent of returns. Turnout had been very high, at nearly 88 percent, according to the electoral commission.

The government urged patience, calling the results a tie and saying it was too early to call.

"We are really talking about a dead heat at the moment. So it would be better to hold your enthusiasm and calmly wait for results," Alvaro Garcia, the country's vice president, told reporters.

"All your celebration may well turn into weeping."

Evo Morales is Bolivia's first indigenous president and has been credited with slashing poverty in one of the region's poorest countries [AP]

If the result is confirmed, it would be another blow for South America's once dominant populist leftist movement that has suffered a series of recent electoral defeats across the continent.

Morales, Bolivia's first indigenous president, has been credited with slashing poverty in one of the region's poorest countries. He took office in 2006 and was re-elected in 2014 with 61 percent of the vote.

But a growing number of critics charge his administration with corruption, waste and authoritarianism.

Recent allegations about an ex-girlfriend whose company won lucrative government contracts have weighed heavily on his popularity.

Economic boom

Morales presided over an unprecedented economic boom as prices for raw materials soared just as he took office. He built airports, highways and the pride of La Paz, an Austrian-built aerial tramway system.

He also put a Chinese-built satellite into space. Average per capita income rose from $873 to $3,119 and a new indigenous middle class was born.

But the boom is over. Bolivia's revenues from natural gas and minerals, making up three-fourths of its exports, were down 32 percent last year.

Source: Agencies