Center-right candidate Ivan Duque, who has vowed to alter a fragile peace deal, took a commanding early lead in Colombia's presidential election today with nearly half of polling stations counted.

With 68.7% of stations counted, Mr Duque had 55.5% of votes, while his leftist rival Gustavo Petro, who has pledged to shake up Colombia's economic model, had 40.4%.

Mr Duque, 41, the business-friendly protege of hardline former President Alvaro Uribe, wants to change a peace deal he deems too lenient on Marxist FARC rebels, while keeping Colombia's largely orthodox economic model.

His opponent, former guerrilla Mr Petro, has pledged to take on political elites, redistribute land to the poor and gradually eliminate the need for oil and coal in Latin America's fourth-largest economy.

"We're between a rock and a hard place," said financial planner Juan Jose Mojica. "They're two extremes that could destroy the development that the country has made over the last years."

From the sweltering Caribbean coast to the frigid heights of the Andes, voting was largely uneventful at the 11,230 polling stations across the nation.

Marking of ballots was monitored by international election observers to guard against any fraud. Results are expected overnight.

Mr Petro, 58, whose policies have prompted rivals to compare him to Venezuela's former socialist president Hugo Chavez, has called on supporters to take to the streets if he feels there was widespread manipulation of the tally.

These are the first elections since a 2016 peace deal with the Revolutionary Armed Forces of Colombia (FARC), which ended their part in a five-decade conflict that has killed more than 220,000 people and displaced millions.