The Datum and Apoyo polling institutes put Mr Humala's support at between 29 and 29.6 per cent, while both Mr Garcia and Ms Flores had around 24 per cent.
CPI had Mr Humala with just over 30 per cent, followed by Ms Flores with 25.8 per cent and Mr Garcia with 24 per cent.
Virtually unknown in political circles until recently, Humala has seen his popularity surge in just weeks.
A tough-talking nationalist who admires Venezuela's firebrand President Hugo Chavez, Humala has become a controversial figure in Peru, loved by some, hated by others.
Election protest
Several hundred protesters hurled eggs and plastic bottles, and chanted "assassin, murderer," as Mr Humala as he cast his ballot at a Lima university.
Riot police were called to clear a path and shield Mr Humala and his wife Nadine as they left the Lima university, where the candidate voted in presidential and legislative elections.
As supporters chanted "Humala president," protesters hurled eggs and plastic bottles and yelled "assassin, murderer."
Allegations that surfaced during the electoral campaign claim that Mr Humala was responsible for the torture and "disappearance" of leftist government opponents in 1992, when he was a military officer. Mr Humala has denied the claims.
Mr Humala was trapped for 35 minutes inside the university before police reinforcements were sent to escort him out.
While in the building, Humala was seen talking to former Canadian foreign minister Lloyd Axworthy, who heads an observer mission of the Organization of American States (OAS.)
He later blamed what he called "a fascist act" on his main rivals Lourdes Flores and Alan Garcia as well as President Alejandro Toledo, saying the three had formed a "united front" against him during the campaign.
Social justice
All three leading candidates have pledged to fight for social justice, but it is Mr Humala who appears to have stirred the imagination of the millions of
impoverished Peruvians who often feel they have not shared in the country's
economic growth.
Mr Humala, 43, has called for a redistribution of wealth and exemplary punishment for crooked politicians he says have poisoned the country.
He wants to tighten state controls over the gas and mining industries and opposes the US-financed eradication of coca, a medicinal herb from which cocaine is
extracted.
His rivals portray him as a dictator in the making who would plunge Peru
into total chaos.
Ms Flores, for her part, is backed by the business community, and has battled
claims she is the candidate of wealthy Peruvians.
A staunch Roman Catholic who opposes abortion, Ms Flores, 46, had already made two unsuccessful bids for the presidency.
Mr Garcia is a gifted orator and former president who has spent much of his
campaign trying to convince voters that he would not repeat past mistakes.