Democratic Center party candidate Ivan Duque won the Colombian presidency in Sunday's runoff vote, election authorities said.

With 99.56 percent of the ballots counted, Duque garnered an unprecedented 10.3 million votes, or 53.95 percent, while his runoff rival, Gustavo Petro with the Colombia Humana movement, received about 8 million votes, or 41.83 percent.

The 41-year-old Duque thus becomes the successor to President Juan Manuel Santos and will take over from him on Aug. 7.

Blank ballots have totaled 4.2 percent so far, or 795,510 votes, significantly below the 15 percent that some surveys had predicted would be cast.

Santos telephoned Duque to congratulate him on his victory, later writing on his Twitter account: "I called Ivan Duque to congratulate him and wish him the best of luck. I offered the government's full cooperation to ensure an orderly and calm transition."

During the campaign, Santos had not expressed his support for either of the two main candidates, who on Sunday he called "opponents" of his administration.

Santos after voting in Bogota called the process a "momentous election," highlighting the fact that it was held in peace.

"In the last election's first round, a former FARC commander voted democratically for the first time ever," Santos said, referring to guerrilla chief-turned-political party leader, Rodrigo Londoño.

Duque - who had remained ahead in the polls in the run-up to Sunday's vote - received the backing of former President Alvaro Uribe, who said after casting his ballot that the Democratic Center party leader will protect Colombia.

"I voted for them (Duque and running mate Marta Lucia Ramirez) because they guarantee socially inclusive growth," Uribe said. "They are a guarantee that Colombia will not fall into the destructive clutches of socialism."

More than 7.5 million Colombians voted for Duque in the May 27 first-round election, while Petro received 4.8 million votes, which translates to 39.14 percent and 25.08 percent, respectively.

Authorities expect a peaceful election fostered not only by the standing peace agreement with the FARC, but also due to the five-day cease-fire ordered by the National Liberation Army (ELN) rebels.