Pedro Pablo Kuczynski is on track to become Peru's next president after a near-final vote tally gave him a narrow lead in the country's tightest election in decades, although his rival Keiko Fujimori has yet to accept defeat.
Outgoing President Ollanta Humala and the leaders of Colombia, Chile and Argentina congratulated Kuczynski, a former investment banker, after the results were announced on Thursday.
The centrist economist said he would wait for a complete count before claiming victory as thousands of disputed or unclear ballots remain uncounted.
A mere 41,964 votes separated the two business-friendly candidates, underscoring the divisive legacy of Fujimori's father, imprisoned former authoritarian leader Alberto Fujimori.
The gap has fluctuated somewhat in recent days, but Fujimori has trailed throughout the vote count.
"We take this virtual verdict with much modesty because Peru has many challenges ahead," Kuczynski, 77, said in a news conference as supporters cheered him.
Kuczynski won 50.12 per cent of all tallied votes while Fujimori had 49.88 per cent, the electoral office ONPE said.
However, 0.2 per cent of ballots had been questioned and could not be counted.
Members of Fujimori's conservative party said earlier that electoral authorities should annul bundles of ballots, some of which had already been included in official tallies, because they had detected irregularities at several polling stations.
The lawmakers said they would accept the official results, however.
The head of ONPE said disputed ballots would be settled by special electoral panels "soon".
About 152 bundles of ballots remained under review by authorities late on Thursday. However, with each bundle holding up to 300 votes, they would only be enough to offset Kuczynski's lead if nearly all were decided in Fujimori's favour.
It would be Fujimori's second consecutive narrow loss in a presidential run-off race, after outgoing Humala defeated her in 2011. Humala could not run again because of term limits.
On the campaign trail, Fujimori tried to distance herself from the controversial policies and actions of her father, who is now 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 policies that the elder Fujimori introduced in the early 1990s and that three successive democratic governments kept intact in the global minerals exporter.
A former prime minister and the son of European immigrants, Kuczynski is more liberal on social issues than Fujimori. He promises to secure investment for infrastructure projects that would restore growth to Peru's economy.
