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http://news.bbc.co.uk/2/hi/americas/8397908.stmMr Morales said that "by holding two-thirds of Congress it now is my duty to accelerate the pace of change".
Official results are expected in the coming days.
Foreign observers have praised the election for its transparency and fairness.
Mr Morales's support base is chiefly among poor indigenous people who account for some 65% of the population - in contrast to his challengers.
"He's changing things. He's helping the poor and building highways and schools," Veronica Canizaya, a 49-year-old housewife, told Reuters news agency before casting her vote at a public school on the shores of Lake Titicaca.
Analysts say a victory for Mr Morales will solidify his dominance in Bolivian politics and weaken the split conservative opposition tied to the business elite.
His other challenger was Samuel Doria Medina, a wealthy businessman.
Both challengers accused Mr Morales of having "totalitarian" ambitions for the country and of being responsible for the rise in cocaine production, says our correspondent, Andres Schipani.
Mr Morales told crowds at his final campaign rally: "There are two roads: continue with change or return to the past."