Ecuador's national electoral council on Sunday declared President Daniel Noboa the winner of the country's presidential race, after he held a steady and unexpectedly wide 12-point lead over leftist Luisa Gonzalez throughout the count.

Gonzalez told chanting supporters she does not accept the results and will demand a recount, calling it "the worst and most grotesque electoral fraud in the history of Ecuador."

With nearly 93% of ballot boxes counted, Noboa had 55.8% of votes, compared to Gonzalez's 44.1%, a difference of more than one million votes.

The results were a sharp contrast to the February first round, where Noboa finished just 16,746 votes ahead of Gonzalez.

"We inform the Ecuadorean people that with more than 90% of the ballot boxes processed nationally, there is an irreversible trend in the second round of voting," Diana Atamaint, the head of the national electoral council, said in a statement to the press. "The winning duo is Daniel Noboa Azin and (vice president-elect) Maria Jose Pinto."

Gonzalez expressed disbelief over the results to chanting supporters in Quito.

"I refuse to believe that a people would prefer lies instead of truth, violence instead of peace and unity," Gonzalez said. "We are going to demand a recount and for them to open ballot boxes."

The candidates and Gonzalez's mentor, former President Rafael Correa, had urged some 90,000 polling-place observers to guard against electoral fraud.

Correa said on social media that the results were "impossible".

Meanwhile, Noboa, a 37-year-old business heir, said in remarks from the beach town of Olon that there was no doubt about his victory as he thanked supporters.