Philippines' president-elect Rodrigo Duterte is planning to visit the Vatican to make a personal apology to the Pope for calling him a "son of a whore", his spokesman says.

Key points: Duterte had called Pope Francis "son of a whore" over traffic jams in Manila

Duterte had called Pope Francis "son of a whore" over traffic jams in Manila Has already apologised in a letter but is now planning to visit the Vatican

Has already apologised in a letter but is now planning to visit the Vatican His gutter language was "a performance to attract voters" attention, his spokesman says

Mr Duterte, the long-time Mayor of Davao, surged to a landslide election win on Monday following an incendiary campaign in which he gleefully used foul language to disrespect authority figures.

"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," Peter Lavina said.

In a rambling speech to announce his presidential run, Mr Duterte lashed out at Pope Francis for causing traffic jams in Manila when he visited the mainly Catholic nation last year.

"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'," Mr Duterte said.

Catholic leaders in the Philippines condemned Mr Duterte's comments but, like many other controversial remarks, they had little impact on his popularity.

Mr Duterte had already apologised to the Pope in a letter and received a response from the Vatican offering "the assurance of prayers", his aides said on the campaign trail.

He said publicly the Pope was the victim of a "stray bullet" resulting from his gutter language and frustration with government incompetence.

Mr Lavina said no schedule had yet been set for the Vatican trip, although it was a top priority.

Lavina has said repeatedly in recent days that Mr Duterte plans to adopt a more moderate and presidential tone when he assumes office, and that his gutter language and insults were part of a performance to attract voters' attention.

"You have to understand the Philippine style of elections. The context is most of our politicians need to communicate to our audience so many of our politicians sing and dance," Mr Lavina said.

"Some make jokes, some make funny faces. Some dress outrageously. So it is all in this context that all these jokes, bantering, happen during the campaign. We don't expect the same attitude of our officials thereafter."

Mr Lavina was explaining a joke Mr Duterte made about burning Singapore's flag, which provoked an angry response from the city-state's embassy.

Other campaign firebombs included saying he wanted to rape a "beautiful" Australian missionary who was sexually assaulted and murdered in a 1989 prison riot in Davao.

Mr Duterte made his controversial rape comments as he recounted at a campaign rally the 1989 riot, in which he said he personally shot dead some of the inmate instigators.

Mr Duterte also stirred diplomatic anger when he warned that he was prepared to sever ties with the United States and Australia, two of the Philippines' longest and most important allies.

He was reacting to criticism from the US and Australian ambassadors over his rape comments, and told them to "shut their mouths".

Mr Duterte is due to be sworn into office on June 30 for a term of six years.

AFP