Voting for a new Philippine president began on Monday after an acrimonious election campaign that revealed popular disgust with the country's ruling elite for failing to tackle poverty and inequality despite years of robust economic growth.

Opinion polls in the days ahead of the vote showed that Rodrigo Duterte - a mayor whose brash challenge to the political establishment has drawn comparisons with U.S. presidential candidate Donald Trump - was comfortably ahead of his four rivals for the presidency.

"I am voting early so the mayor will be represented," said housewife Lea Alimasag at a polling station in the southern city of 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 color of the Duterte camp.

The populist mayor's single-issue campaign focused on law and order tapped into 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 favored candidate of outgoing President Benigno Aquino, described the election as "the force of democracy against the force of dictatorship."

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

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

Clamor for Change

More than half of the Southeast Asian nation's 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.

Some campaign strategists have expressed concern that, with so much at stake and the possibility of a close race, vote-buying could be a problem in Monday's ballot.

Polls opened at 6 a.m. (2200 GMT on Sunday) and will close 11 hours later. The election commission chief has said results could be known within 24 hours but it may take up to three days