Philippine President Rodrigo's daughter would run for president in next year's election and her father's long-time aide, who filed his vice presidential candidacy, would be her running mate, broadcasting firm ABS-CBN news reported late on Saturday.

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

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

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 was quoted as saying.

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 being abused.

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

Political analysts were sceptical, noting that last-minute changes were still possible, as in 2015 when Duterte entered the presidential election race at the eleventh hour and won by a huge margin, and Duterte-Carpio, they said, could do the same.

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