Colombians headed to the polls Sunday in a closely watched presidential election that could redefine the country’s approach to rising violence by drug-running guerrillas, either staying left and opting for dialogue or moving right towards all-out war.

Pre-election polls showed left-wing senator Ivan Cepeda riding high on strong support for combative outgoing President Gustavo Petro, but he faces a challenge from hard-right lawyer Abelardo de la Espriella and conservative senator Paloma Valencia.

If, as expected, no candidate wins an outright majority on Sunday, a run-off between the two poll-toppers will be held on June 21.

The election is widely seen as a referendum on the "total peace" strategy of Petro, Colombia's first left-wing president, who tried but failed to convince guerrilla groups that rejected a landmark 2016 peace deal to finally lay down arms.

Despite his absence from the ballot, "the campaign revolves around Petro," said Yann Basset, political science professor at Bogota's University of Rosario. "He's at the center of all the discussions."