Voting for a new Philippine president began on Monday with a brash challenger to the political establishment the favourite to win after campaigning on pledges to crush crime and corruption.

Many voters in Manila had to line up in blazing sunshine for more than an hour to cast their votes, and there were several reports of electronic voting machine hitches, which could dash the election commission's hope to declare a victor in 24 hours.

The election campaign exposed widespread disgust with the Southeast Asian country's ruling elite for failing to tackle poverty and inequality despite years of robust economic growth.

Tapping into that sentiment, Rodrigo Duterte, mayor of the southern city of Davao, emerged as the front runner by brazenly defying political tradition, much as Republican presidential candidate Donald Trump has done in the US.

"I am voting early so the mayor will be represented," said housewife Lea Alimasag at a polling station in Davao, where Duterte's man-of-the-people style has won him seven mayoral elections since 1988. Like many others there, she was dressed in red, the official colour of the Duterte camp.

The populist mayor's single-issue campaign focused on law and order chimed with popular anxiety about graft, crime and drug abuse, but for many his incendiary rhetoric and talk of extrajudicial killings smack worryingly of the country's authoritarian past.

"Mr Duterte's campaign symbol is a fist - intended for lawbreakers, but seemingly also aimed at the oligarchy," Miguel Syjuco, a respected Philippine writer, said in an opinion column last week. "The message resonates with the frustrated poor who feel let down by the government, but his fans span all classes."

He said Duterte's "change is coming" slogan was "the exactly right message from the completely wrong messenger".

Manuel Roxas, the grandson of a former president and the favoured candidate of outgoing President Benigno Aquino, described the election as "the force of democracy against the force of dictatorship".

Jordan Manalo, a 24-year-old hotel employee in Manila who was queuing to cast his ballot, said he was for Duterte.

"If we have to go extreme, why not? I want someone new, someone who would go beyond the usual. I don't care if he does not look elite ... I am here for my country and that is what I care about."

Despite concerns about Duterte, global risk research firm Eurasia Group said in a pre-election report that the Philippines was likely to continue on Aquino's pro-growth and reform-oriented path regardless of who wins the presidency.

Under Aquino, the annual economic growth rate has averaged around 6 percent, one of the highest in Asia.

CLAMOUR FOR CHANGE

More than half of the population of 100 million people are registered to vote in the election to choose a president, vice-president, 300 lawmakers and about 18,000 local government officials.

Jostling for office with traditional politicians, voters will find business chiefs, entertainment personalities and the global boxing icon Manny Pacquiao, who is running for the Senate.

"Bongbong" Marcos Jr., the son and namesake of late dictator Ferdinand Marcos, is contesting the vice presidency.

Elections in the Philippines are traditionally difficult to predict, but two opinion polls last week showed Duterte had a lead of 11 percentage points over his nearest rival, with support from across all socioeconomic demographic groups.

Grace Poe, a senator, and Roxas are seen as the most likely to challenge Duterte. Poe's pro-poor platform has resonated among Filipinos, as has her life story: abandoned at a church as a baby and adopted by movie stars.

Aquino last week urged trailing candidates to unite and block Duterte's path to the presidency. Interpreting that plea as a call for her to withdraw and back Roxas, Poe refused. - Reuters