Ex-Wall Street banker Pedro Pablo Kuczynski's camp claimed victory in Peru's presidential election, but polarising rival Keiko Fujimori said it is not over till the last vote is counted.

Peru's election: Media, money and manipulation - The Listening Post (Full)

With more than 97 percent of the ballots in from Sunday's runoff, the Oxford-trained economist known as "PPK" had the edge in the race to lead one of Latin America's fastest-growing economies: 50.14 percent of the vote to 49.86 percent for Fujimori, the daughter of jailed ex-president Alberto Fujimori.

Kuczynski's running mate, Martin Vizcarra, declared victory.

"This result is irreversible," he told RPP TV, as the national elections office ONPE tallied the last ballots from remote areas and overseas.

"Even if the ONPE hasn't filled in the missing numbers, our people on the ground have copies of the result sheets and that enables us to calculate that PPK will win."

WATCH: Peru election - Pedro Kuczynski holds slight lead as votes counted

With fewer than 50,000 votes separating the candidates, electoral officials said it could take until Thursday to deliver a final result.

Bad weather has grounded flights meant to deliver results from the Amazon jungle region, and some have had to be sent by boat.

Peru's presidential poll: Poor ask for real change

Kuczynski, 77, has said he will not declare victory until the official verdict is in.

Fujimori, 41, was hunkered down in her campaign headquarters for a second straight day.

Her campaign is hoping she will win heavily in remote areas still sending in their results thanks to her father's pull with poor rural voters.

Both candidates are right-leaning, US-educated politicians from immigrant families.

They vowed to fight crime and create jobs in the nation of 31 million people, a major source of gold, copper - and cocaine.

Famed for its ancient Incan ruins high in the Andes mountains and its fusion-fuelled cuisine, symbolised by the refreshing raw fish dish ceviche, Peru has been one of Latin America's best-performing economies.

Source: AFP