MANILA (REUTERS) - The daughter of Philippine leader Rodrigo Duterte remains the most popular prospect for next year's presidential election, an opinion poll showed on Wednesday (Sept 29), 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 per cent to 20 per cent.

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

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

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 per cent from 18 per cent.

Sotto, a former actor and comedian, won 25 per cent support, a big jump from his 10 per cent 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 per cent of 1,200 respondents believed his move violates the intention of the constitution, which has a one-term limit to prevent abuse of power.