Six million Bolivians were casting ballots in the presidential and congressional polls, which would likely expose the weakness of a fragmented opposition.
Voting -- which is compulsory -- began on schedule at 8:00 am (1730 IST) and was to end at 4:00 pm. Alcohol consumption was prohibited 48 hours before and 12 hours after polling. Carrying firearms was also banned during the vote.
Morales, who has blended leftwing economic policy with nationalist rhetoric and a focus on indigenous rights and the environment -- all while presiding over an economic boom -- was seen to have 59 per cent support heading into the election, according to surveys.
Morales stands to extend his time in office to 14 years, until January 2020, after Bolivia's Supreme Court ruled last year that his first term was exempt from a new constitution adopted in 2009 that imposed a limit of one reelection for sitting presidents.
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"El Evo," as he is often called in Bolivia, looks virtually guaranteed to win in a single round.
His Movement Toward Socialism (MAS) was meanwhile on track to win a two-thirds majority in the Senate and possibly in the Chamber of Deputies as well, according to opinion polls.
His government has nationalised a broad range of sectors including oil, gas, mining, telecommunications and water, rolled out welfare grants for the elderly, children and expectant mothers, and moved to empower previously marginalised groups, including the 65 per cent of the population that is indigenous.
Defying opponents' dire warnings of economic catastrophe, Bolivia has instead seen a boom.
GDP grew 6.8 per cent last year and is forecast to grow more than five per cent this year, one of the fastest rates in Latin America.