Firebrand Philippine city mayor Rodrigo Duterte took a commanding lead as unofficial presidential election results poured in on Monday, suggesting the political outsider's pledges to crush crime and corruption had carried the day.

Three hours after polling stations had closed, a rolling ballot count by an election commission-accredited watchdog showed about 40 percent of the votes cast were in his favour. An exit poll of a small number of voters showed a similar lead.

Asked by a television interviewer what he thought about his apparent victory, Duterte gave a puzzling answer.

"Sometimes I'm victorious and the winner, sometimes there's always losing and being sad, sometimes being sick and healthy," he told CNN Philippines, slouched in a chair and dressed casually in a checked, short-sleeve shirt.

"That is how the universe is being played every day."

The 71-year-old's defiance of political tradition has drawn comparisons with US Republican presidential candidate Donald Trump, as has his regular references to his libido.

His man-of-the-people demeanour tapped into popular disgust with the political establishment over its failure to tackle poverty and inequality despite several uninterrupted years of robust economic growth.

His incendiary rhetoric and advocacy of extrajudicial killings to stamp out crime and drugs have, however, alarmed many who hear echoes of the Southeast Asian country's authoritarian past.

The election numbers reported by the Parish Pastoral Council for Responsible Voting (PPCRV) had, by 1208 GMT, accounted for about 60 percent of the 54 million registered Filipino voters.

Duterte had 10.4 million votes, with Senator Grace Poe a distant second with 5.9 million. The government's candidate, Manuel Roxas, was just behind Poe with 5.8 million.

VIRULENT CAMPAIGN

The presidential race has been one of the most divisive in years, with outgoing leader Benigno Aquino and rival candidates warning of a disaster if Duterte makes good on his promises.

He had been acting uncharacteristically coy for most of the day and had earlier urged the throng of media to stop asking him about the possibility of winning.

He talked of making peace with his rivals after a "virulent" campaign and reiterated that if president, he would give police a green light to use deadly force against criminals.

"If they put up a good fight and refuse to surrender and if you feel your life is in jeopardy, shoot. You have my authority," he said in Davao City, where he has been mayor for 22 years.

At least 11 people were killed in violence before voting started, but otherwise the election was mostly smooth with voting machine problems at only a few dozen polling stations.

Voters also cast ballots for the vice-president, 300 lawmakers and about 18,000 local government officials.

"Bongbong" Marcos Jr., the son and namesake of late dictator Ferdinand Marcos, looked on course to become vice president with a narrow lead as the votes were being counted.

Duterte's entertaining speeches, often loaded with profanity, have shed little light on his policies beyond going after gangsters and drug pushers.

He has been vague on what he would do to spur an economy that has averaged growth at around 6 percent under Aquino.

In a report on Monday, ratings agency S&P Global said a Duterte presidency would create uncertainty, especially if he picks fights with the political elite.

"He could take some time getting used to the many compromises required in the national leadership position," it said. - Reuters