In a remarkable change of tone, presumptive Philippine president Rodrigo Duterte said he plans to visit the Vatican to make a personal apology to Pope Francis for having called him a "son of a whore."

"The mayor repeatedly said he wants to visit the Vatican, win or lose, not only to pay homage to the Pope but he really needs to explain to the Pope and ask for forgiveness," Duterte's spokesman Peter Lavina told reporters in Davao City on Thursday, Agence France Presse (AFP) reports.

This developed as the United States, China and the European Union all extended a hand of friendship to the incoming Philippine president, saying they respect the will of the Filipino people and look forward to congratulating him upon his formal assumption of power, according to the Philippine Daily Inquirer and other sources.

Duterte, the longtime mayor of Davao City on the southern Philippine island of Mindanao, is awaiting a formal declaration of his victory in the May 9 presidential election after unofficial vote count showed him winning the race by a landslide.

With 95.87 percent of polling precincts reporting as of Friday morning, Duterte leads the unofficial vote count with 15,915,762 votes (38.5 percent), way ahead of his closest rival Mar Roxas with 9,681,762 votes (23.5 percent), data from the Commission on Elections showed.

In a speech last year, Duterte lashed out at Pope Francis for causing traffic jams in Manila when the head of the Roman Catholic Church visited the predominantly Catholic nation.

"It took us five hours to get from the hotel to the airport. I asked who was coming. They said it was the pope. I wanted to call him: 'Pope, son of a whore, go home. Don't visit anymore'," Duterte was quoted as saying then.

Philippine Catholic leaders quickly condemned Duterte's comments and expressed their opposition to his candidacy.

However, the Catholic opposition and other controversies sparked by Duterte's incendiary campaign rhetoric had little effect on the candidate's mass appeal.

The controversies included Duterte's remark that he wanted to rape a "beautiful" Australian missionary who was sexually assaulted and murdered in a 1989 prison riot in Davao.

He also called many of his opponents and critics, including current President Benigno Aquino III, as "son of a whore" in Tagalog, the main Philippine language.

Duterte also vowed repeatedly that he would kill tens of thousands of suspected criminals in an unprecedented law-and-order crackdown, boasting that he would feed their bodies to the fish in Manila Bay.

According to his aides, Duterte had already apologised to the Pope in a formal letter and that the Vatican had responded, offering "the assurance of prayers."

Duterte recently said he did not mean to offend the Pope, adding that the latter was just the victim of a "stray bullet" resulting from his gutter language and frustration with government incompetence.

No date has been set for Duterte's Vatican trip, although it was a top priority, his aides said.

Duterte is set to be sworn into office on June 30 and will serve as president for a term of six years.

Duterte will adopt a more moderate and presidential tone when he assumes office, his spokesman said, adding that his foul language was just part of a performance to attract voters' attention.