Philippine President Rodrigo Duterte's daughter will run for president in the 2022 election and her father's long-time aide, who has filed his vice-presidential candidacy, will be her running mate, ABS-CBN news reported late on Saturday.

Sara Duterte-Carpio is currently mayor of Davao, the Philippines' third-largest city, and on Saturday filed her candidacy to run again for mayor. She has previously said she would not run for national office next year.

ABS-CBN news based its report on an interview that president Duterte had with a broadcast journalist right after he announced that he was retiring from politics on Saturday, while accompanying his closest loyalist Senator Christopher "Bong" Go to file his vice-presidential candidacy.

He was asked: "So is it clear, Sara-Go?"

"It is Sara-Go," Duterte said in response.

When asked to confirm what the president said, Duterte-Carpio's spokesperson Mayor Christina Garcia Frasco told Reuters: "The extent of my knowledge is also what was reported in local news. We have no comment on the same."

Go did not immediately respond to a Reuters request for comment.

Sara strong choice, Go risky

ABS-CBN news said it obtained permission from the broadcast journalist to use the video showing Duterte outside a hotel in Manila where the registration of candidates was taking place and that a transcript was also provided.

In the same clip, Duterte was asked when his daughter would file her candidacy for president, he said: "I really do not know. I do not have any idea at all".

Asked if he had given his daughter permission to run for president, he said: "Ah, no, actually we don't talk about politics, ever since we never talk about politics. I would say that it is for the better."

Duterte's political party has yet to officially nominate its presidential candidate and Duterte-Carpio belongs to a different party.

Retired political science professor Temario Rivera said while Duterte's daughter is winnable, the same could not be said about Go, who has no political base, thus making a Duterte-Carpio-Go ticket "weak".

"It would be an unsound political decision because what can Bong Go add to Sara's candidacy?" Rivera said.

While Duterte-Carpio is by far the most popular presidential prospect, according to successive opinion polls this year, Go, who was the president's long-time aide before he became senator, trails in opinion surveys on preferred vice-presidential bets.

Loyal successor crucial

Duterte, 76, said on Saturday he was retiring from politics, a surprise move that fuelled speculation he was clearing the way for a presidential run by his daughter.

He had been expected to run for the No 2 job, a plan most Filipinos oppose as violating the spirit of the constitution which sets a one-term limit for the president to stop power from being abused.

Duterte-Carpio's mayorial re-election filing did little to douse speculation she has her eye on the presidency.

Analysts say it is crucial for Duterte to have a loyal successor to insulate him from potential legal action - at home or by the International Criminal Court - over the thousands of state killings in his war on drugs since 2016.

Candidates have until Oct 8 to register, but withdrawals and substitutions are allowed until Nov 15, leaving scope for last-minute changes of heart.

- Reuters