Leftist ex-military man Ollanta Humala looked set to win Peru's presidency, according to first estimates, after a tight battle with Keiko Fujimori, heir to a jailed, authoritarian ex-president.

Supporters of the 48-year-old former lieutenant colonel Humala, who just lost out in the 2006 election, cheered as the first results came in and gathered holding red and white Peruvian flags in a main Lima square.

Humala won between 51 and 52.2 percent in four quick counts of 100 percent of the vote against 47.8-49 for his 36-year-old right-wing rival Fujimori, several hours after the vote's close at 4:00 pm (2100 GMT).

The estimates, from pollsters Datum, Ipsos-Apoyo, CPI and watchdog Transparencia, had a margin of error of one percent. Transparencia said the elections generally took place without serious incident.

Humala's victory "is irreversible," Manuel Saavedra, director of CPI, told AFP.

After a bitter campaign, many were faced with a choice for the "lesser of two evils" after the two most extreme candidates won an April first round in the Andean nation of 29 million stretching from the Pacific to the Amazon.

Humala campaigned on promises of sharing out Peru's rich mineral wealth after a decade of record growth and sought to play down former ties to the radical socialism of Venezuelan President Hugo Chavez.

His victory would be the first return of the left to power in Peru since the 1968-1975 military regime of Juan Velasco Alvaredo.

Keiko Fujimori campaigned in the shadow of her father, Alberto Fujimori, who is serving a 25-year jail term for corruption and rights abuses during a 1990s crackdown on extreme leftist Shining Path and Tupac Amaru guerrillas. His fans remember him for the crackdown and for reining in hyperinflation.

Nobel Prize-winning author Mario Vargas Llosa, who backed Humala to block Fujimori, already told Lima's CPN radio Sunday that "it was a defeat of fascism, we have to celebrate it as a great victory of democracy in Peru. The important thing is that a dictatorship did not return to power."

Both Fujimori and Humala drew support with populist promises to help around one third of the population still living in poverty despite Peru's unprecedented growth in the past decade.

Humala's pledges to increase control of the mining sector sent shockwaves through Lima's stock exchange, and he moderated his platform through the campaign, turning toward the moderate left of Brazil.

He first came to prominence in 2000 when he led a short-lived military rebellion at the end of Alberto Fujimori's 1990-2000 elected presidency. He has also been accused of rights abuses which have never been proved.

Fujimori wooed investors, most of the media, and conservative ex-presidential candidates with promises of keeping the free-market model which has helped make Peru one of Latin America's fastest growing economies.

Surrounded by many of her father's allies, she has failed to convince detractors that she would not follow in his footsteps and possibly seek to free him. Keiko Fujimori also served as Peru's "first lady" aged 19 following her parents' bitter separation.

Both candidates sought to remove doubts over their credibility in the tight race.

Luis Alberto Guzman, a 49-year-old technician, said he voted for Humala, because "we need a change. The powerful take all the money coming in and nothing's left for the poor."

Five soldiers deployed to provide election security were killed and six hurt in an attack Saturday blamed on leftist Shining Path guerrillas linked to drug traffickers in southeast Peru. Humala vowed to fight the remnants of the Shining Path, who work with drug traffickers in remote areas of the Andes.

If his victory is confirmed, Humala will take over from President Alan Garcia on July 28.

He will face tough negotiations over his political platform in the Congress, where his nationalist party has only 47 seats out of 130.