Former World Bank economist Pedro Pablo Kuczynski won 41,438 more votes than Keiko Fujimori in Peru's photo finish presidential election, but thousands of disputed or unclear ballots remain uncounted, authorities said on Thursday.

Kuczynski, a centrist, won 50.12 percent of all tallied votes over 49.88 percent for Keiko Fujimori, the daughter of a jailed former president, the ONPE electoral office said.

It was the Andean nation's tightest election in half a century.

Kuczynski, 77, said he would wait for final results from ONPE before claiming victory, but he addressed Peruvians as though he had won.

"We're going to work for all Peruvians," Kuczynski told a news conference. "Many Peruvians feel that the train has passed them by, but we want everyone to get on board right away."

The head of ONPE said the issue of disputed and uncounted ballots would be settled "soon" but did not give details.

Fujimori did not concede defeat after Thursday's official tally was announced. While the numbers have fluctuated somewhat in recent days, she has not been ahead of Kuczynski since vote counting started.

Her allies in Congress said earlier they wanted electoral authorities to annul bundles of ballots from various different voting stations because they had detected irregularities. The lawmakers said they would accept the official results, however.

About 170 such bundles have been questioned. However, even with each bundle holding up to 300 votes, they would only be enough to counter Kuczynski's lead if nearly all were decided in Fujimori's favor.

It appeared to be Fujimori's second consecutive loss in a presidential runoff race, after outgoing President Ollanta Humala defeated her in 2011. Humala was constitutionally barred from running for a second consecutive term.

On the campaign trail, Fujimori tried to distance herself from the darker deeds of her father Alberto Fujimori, who is serving a 25-year sentence for graft and human rights abuses during his 1990-2000 rule. But she never acknowledged he committed any crimes.

Both Kuczynski and Fujimori promised to continue the free-market polices that her father introduced in the early 1990s and that three successive democratic governments kept intact.

A former prime minister and the son of European immigrants, Kuczynski is liberal on social issues and favors same sex civil unions. He dismissed Fujimori's hard-line proposals on crime, including building high-altitude prisons, as myopic.