Anti-establishment firebrand Rodrigo Duterte was set to secure a huge win in Monday's Philippine presidential elections, according to a poll monitor, after an incendiary campaign dominated by his profanity-laced vows to kill criminals.

Duterte, the longtime mayor of the southern city of Davao, hypnotised millions with his vows of brutal but quick solutions to the nation's twin plagues of crime and poverty, which many believed had worsened despite strong economic growth in recent years.

And after a record turnout of voters in Monday's elections, Duterte appeared set for a commanding victory.

With 80 percent of the vote counted late on Monday night, Duterte had 13.2 million votes, about 5.5 million more than his nearest rival, according to the PPCRV, a Catholic Church-run poll monitor accredited by the government to tally the votes.

Duterte had 38.72 percent of the vote, with administration candidate Mar Roxas in second place with 22.67 percent.

Senator Grace Poe, the adopted daughter of movie stars, conceded after the ongoing tally placed her third with 21.87 percent.

"I congratulate Mayor Duterte," Poe told reporters.

"(He) is clearly the leading candidate in the ongoing count and has been chosen by a plurality of our people".

Before the results came out, Duterte was already speaking like a winner as he called for rivalries to be put aside following one of the nation's most bitter and divisive campaigns in the Philippines' history.

"I want to reach out my hand and let us begin the healing now," Duterte told reporters in Davao, the nation's third-biggest city, which he has ruled for most of the past two decades.

However, he said he would not proclaim himself the victor until it was official.

"I am not there until I am there, and that is the when last vote is counted and you are declared a winner. At this time it would be presumptuous of me," he said.

In the Philippines, a winner is decided simply by whomever gets the most votes.

- Threats to kill -

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Duterte, a pugnacious 71-year-old, surged from outsider to the top of surveys with cuss-filled vows to kill tens of thousands of criminals, threats to establish one-man rule if lawmakers disobeyed him and promises to embrace communist rebels.

He also boasted repeatedly about his Viagra-fuelled affairs, while promising voters his mistresses would not cost a lot because he kept them in cheap boarding houses and took them to short-stay hotels for sex.

Duterte caused further disgust in international diplomatic circles with a joke that he wanted to rape a "beautiful" Australian missionary who was killed in a 1989 Philippine prison riot, and by calling the pope a "son of a whore".

Departing President Benigno Aquino, whose mother led the democracy movement that ousted Ferdinand Marcos three decades ago, had warned repeatedly the nation was at risk of succumbing to another dictatorship.

"I need your help to stop the return of terror in our land. I cannot do it alone," Aquino said in an appeal to voters in a final rally on Saturday in Manila for Roxas, his preferred successor and fellow Liberal Party stalwart.

In his final rally on Saturday, Duterte repeated to tens of thousands of cheering fans his plans to end crime within six months of starting his presidency.

"Forget the laws on human rights," said Duterte, who has been accused of running vigilante death squads in Davao.

"If I make it to the presidential palace, I will do just what I did as mayor. You drug pushers, hold-up men and do-nothings, you better go out. Because as the mayor, I'd kill you."

- Elite rule -

Aquino, who is limited by the constitution to a single term of six years, had overseen average annual economic growth of six percent and won international plaudits for trying to tackle corruption.

However, his critics said he had done little to change an economic model that favours an extraordinarily small number of families that control nearly all key industries, and has led to one of Asia's biggest rich-poor divides.

This criticism appeared to have hurt Roxas, a member of the wealthy classes.

Another key message of Duterte's campaign was his pledge to take on the elite, even though his vice presidential running mate was from one of the nation's richest and most powerful families.

Poe had seen her popularity slide after critics pointed to her taking US citizenship then later giving it up.

Vice President Jejomar Binay, the early favourite, was in a distant fourth place, according to the poll monitor, after crumbling under the weight of a barrage of corruption allegations.

In an intriguing sub-plot, former dictator Marcos's son and namesake had a slight lead in the race to be elected vice president, according to the poll monitor, which would cement a remarkable political comeback for his family.