Evo Morales, seeking a controversial fourth term, led Bolivia's presidential election race on Sunday but faces a historic second round run-off against opposition rival Carlos Mesa, partial results showed.

Mr Morales had 45 percent of the vote to Mr Mesa's 38 percent, the Supreme Electoral Tribunal announced, with most of the votes counted.

Elected Bolivia's first indigenous president in 2005, Mr Morales has won his previous elections in the first round, never having to contest a run-off.

The former coca farmer and leftist union leader has led the poor but resource-rich Latin American country for the past 13 years, though his popularity has waned amid allegations of corruption and authoritarianism.

He will face a stiff challenge from Mr Mesa, a 66-year-old former president who led Bolivia from 2001-2005.

Mr Mesa celebrated "an unquestionable triumph" in getting to the second round, amid cheers from his supporters at his La Paz headquarters.

Mr Morales welcomed his first-round win, telling cheering crowds "we have won again, really, it is something historical, unforgettable".

South Korean-born evangelical pastor, Chi Hyun Chung, was the surprise package of the election, polling strongly to finish in third place with 8.7 percent.