The daughter of Philippine leader Rodrigo Duterte remains the most popular prospect for next year's presidential election, an opinion poll showed on Wednesday, while her father slipped into second among contenders for the vice-presidency.

Sara Duterte-Carpio, who this month said she would not seek higher office, has topped all surveys on prospective candidates ahead of registration, which opens on Friday. Her father cannot run for a second term and will seek the vice presidency.

But other potential candidates cut into Duterte-Carpio's lead in the Pulse Asia survey of 2,400 people, held earlier this month, with her support dropping from 28% to 20%.

Boxer Manny Pacquiao, who announced his retirement from the sport on Wednesday to run for the presidency, rose one notch to fourth, with 12% support, up from 8% previously.

Ahead of Pacquiao with 15% was the son and namesake of late dictator Ferdinand Marcos, who has yet to confirm his plans, plus Manila mayor Francisco Domagoso, with 13%.

The same poll showed Senate speaker Vicente Sotto overtaking Duterte as the top contender to become vice president, which in the Philippines is a separate contest. Duterte dropped to 14% from 18%.

Sotto, a former actor and comedian, won 25% support, a big jump from his 10% in the previous poll.

Duterte's decision to seek the largely ceremonial position has been met with skepticism, with critics convinced he has ambitions to retain power, or remain in high office to stymie possible legal action over thousands of state killings during his notorious war on drugs.

Duterte said he wants to serve the public.

A separate survey released this week by Social Weather Stations showed 60% of 1,200 respondents believed his move violates the intention of the constitution, which has a one-term limit to prevent abuse of power.