Colombian President Juan Manuel Santos vowed to bring peace to Colombia after winning re-election on Sunday, telling rebels his victory shows that voters demand an end to five decades of war.

Santos, a center-rightist who has staked his reputation on securing a peace deal with the Revolutionary Armed Forces of Colombia, won almost 51 percent support in the run-off election on Sunday. His right-wing rival Oscar Ivan Zuluaga trailed with 45 percent.

The election divided Colombia between voters who support a deal to end Latin America's longest-running insurgency and Zuluaga's backers who want to force the rebels into a battlefield surrender.

"This is the end of more than 50 years of violence and the start of a new Colombia," Santos said after his election victory, holding up a hand daubed with the word "peace" and wearing a trademark pin of a white dove on his lapel. "A Colombia at peace with itself".

Santos opened talks with the FARC in late 2012. The conflict has killed more than 200,000 people and forced millions more from their homes.

Last week, Santos also revealed preliminary talks with a smaller rebel group, the National Liberation Army, and he said on Sunday the Colombian people were now insisting on peace.

"The demand is not just for the government. Today's message is for the FARC and the ELN and it's a clear message - this is the end," the president said, surrounded by family.

He will start his second four-year term on Aug 7.

During a bitter campaign, Santos faced a barrage of criticism from Zuluaga and his mentor, former president Alvaro Uribe. They played to the outrage felt by millions of Colombians that FARC leaders could escape prison time and even hold public office as part of a negotiated settlement.

Zuluaga's strong support in the election shows how tough it will be for Santos to win the nation's approval in a future referendum if a peace deal is signed and for it to pass through Congress.

Santos, the son of one of the country's most influential families and a Harvard-educated economist, says he began to dream of leading Colombia toward peace two decades ago.

Learning from the mistakes of previous attempts to end the war, Santos said he promised himself he would not allow the rebels to strengthen their ranks, build up their war chests or take the upper hand over the government.