BANGKOK: A 70-year-old crime fighting mayor who boasts about his womanising and praises the extrajudicial killings of drug dealers has emerged as a leading contender for the Philippine presidency.

Rodrigo Duterte, a seven-time mayor of the southern city of Davao who basks in the nickname "the Punisher", has pledged to ruthlessly wipe out crime if he wins next year's election that has been shaken-up by the disqualification of leading candidate Grace Poe.

Mr Duterte warned criminals that if he becomes president "I'll dump all of you into Manila Bay, and fatten all the fish there".

"I do not want to commit a crime but, if by chance, God will place me there, you had better watch out."

Mr Duterte's campaign received a surprise boost on Tuesday when the Philippine electoral commission disqualified Ms Poe for failing to meet residential requirements that includes that candidates must have lived in the country for 10 years.

Polls had shown the 47-year-old adopted daughter of two popular movie stars who was abandoned in a church when she was a baby had been leading the race to be elected president in May.

Mr Duterte built a reputation as a crime fighter who transformed Davao from what was known as the "murder capital of the Philippines" into one of the country's safest and most orderly cities.

He once told criminals that they had two choices about how they left Davao: vertically or horizontally.

"The best practices in the city are the killings (of criminals)," he said on another occasion.

Mr Duterte also assured funeral parlours of brisk business if he wins.

"If I become president, I advise you people to put up several funeral parlour businesses because I am against drugs . . . I might kill someone because of it," he said last week.

When an intoxicated tourist in a bar refused to follow Mr Duterte's anti-smoking law, the mayor reportedly walked up to him, pulled out a .38 revolver and pointed it at the man's crotch.

"You choose, your manhood, or you swallow your cigarette butt."

The man walked out of the bar with his manhood intact.

As he launched his campaign in the devoutly Roman Catholic nation, Mr Duterte bragged about his womanising, telling 10,000 supporters last weekend that he has two wives - without clarifying their legal status - and also two girlfriends.

"If I can love 100 million and one (Filipinos), I can love four women, at the same time," he said.

"If you want me to become president, you should know everything about me."

Mr Duterte said that unlike other politicians he does not use public funds to support his paramours.

"I do not let them live in posh condominium units . . . they just stay in boarding houses," he said.

Analysts say Mr Duterte's crime-busting message will resonate in the crime-weary country but he has already alienated the Catholic Church, the country's most powerful institution.

In January he riled the clergy when he was quoted as cursing traffic delays caused by a visit to the country of Pope Francis.

Mr Duterte initially insisted he was misquoted but then switched focus by claiming that he was sexually abused by a priest as a child.

Archbishop Socrates Villegas responded by accusing Mr Duterte of spreading vulgarity.

"When we find vulgarity funny, we have really become beastly and barbaric as people," the archbishop said.

Other election candidates include Vice-President Jejomar Binay, 73, and former interior minister Mar Roxas, 58.

President Benigno Aquino, who was elected in 2010, is barred from re-contesting the election under the country's constitution.