After denouncing the Catholic Church for its alleged "hypocrisy," presumptive Philippine President Rodrigo Duterte maintained that he believes in God, but that he does not need religion to show his Christian faith.

"I have this deep, abiding faith in God but that does not mean that you have to have a religion, you have to follow somebody, that you have to get a message from this and that," he said over the weekend in Davao City on Mindanao island, where he has been mayor for 20 years.

"Why would I have to go to a human being to whisper my sins and ask for forgiveness from him? Who are you to listen to my sins and give me absolution? You are not God," he said in the press conference covered live by the country's major television networks.

Duterte, who is a Catholic, lashed out at his own Church, calling it the "most hypocritical institution" in the country for claiming moral ascendancy while allegedly engaging in corrupt practices and other wrongdoings.

He said if the Catholic Church excommunicates him for his statements, he might join the Seventh Day Adventists.

The incoming president poured out his grievances on the country's Catholic leadership for campaigning against him before the May 9 election, which he won overwhelmingly. Duterte said the bishops did this even though in his 20 years as mayor of Davao City, priests had been seeking various favours from him, which he said was tantamount to corruption, ABS-CBN News reports.

"They campaigned against me; everybody was saying 'Do not vote for Duterte.' Fine. I said, let this election be a referendum between me and the Catholic Church ... Look, were you able to stop me?" he said.

Duterte referred to the official statement released by the Catholic Bishops Conference of the Philippines (CBCP) on May 1 urging the public to reject a "morally reprehensible" candidate who has shown "scant regard" for the rights of others and the teachings of the Church.

CBCP President Lingayen-Dagupan Archbishop Socrates Villegas has previously criticised Duterte for cursing Pope Francis when the latter visited the Philippine capital Manila in January 2015.

Catholic leaders have also criticised Duterte for openly admitting that he is a womaniser and for his alleged links with a "death squad" known to have summarily executed hundreds of suspected criminals.

Duterte said Catholic Church leaders should not consider themselves morally superior to other people, saying their "hypocritical institution" has a long history of wrongdoing.

He also challenged the bishops to a debate so that he can expose, before assuming office on June 30, the alleged sins of the church.

"You have been castigating me or criticising me. You want a debate before I become president? Okay! ... I will tell you the sins of the Catholic Church beginning from the time the institution of the papacy was established," Duterte said.

The incoming 16th Philippine president also alleged that some bishops, whom he called "sons of whores," had mistresses.

"Do not think you are the moralising agents of the society. As long as you are a human being, you are going to fall down... You're all pageantry," he said.

Duterte also alleged that he was molested by a priest when he was still a child.

He then castigated a bishop who suggested that he should just file a case against his molester. He said the suggestion was "ridiculous" since the priest died 30 years ago and the incident happened during the 1950s.

He said when he assumes office he will defy the Roman Catholic Church and seek to impose a three-child policy in the Philippines.

"I only want three children for every family," Duterte said. "I'm a Christian, but I'm a realist so we have to do something with our overpopulation. I will defy the opinion or the belief of the Church."