Polling stations opened at 1100 GMT on Sunday in what is expected to be a close contest between Colorado Party presidential candidate Santiago Pena, a 44-year-old economist, and 60-year-old political veteran Efrain Alegre, who is leading a broad center-left coalition and pledging a foreign policy shake-up.
Alegre's coalition is aiming to end the almost unbroken, seven-decade hegemony of the ruling conservative Colorado Party in the closest race in many years, Turkish TRT World reported.
Some 4.8 million of the South American country's 7.5 million inhabitants are eligible to vote in the election for president and legislature that will be determined in a single round.
Alegre is leading narrowly in opinion polls amid a recent anti-incumbency trend in Latin American elections.
His main challenger, Pena, is a 44-year-old economist and former finance minister hoping to continue the rule of the Colorado Party that has governed almost continually since 1947.
MNA/PR