The poll signals challenges for the current military-aligned government, with potential voters listing the two main opposition parties as their top two preferences, although many remained undecided.

Paetongtarn Shinawatra, Thaksin's youngest child at age 36, was the choice of 21.6 per cent of respondents in the poll - just behind "undecided", which was cited by 24 per cent of those polled.

The National Institute of Development Administration poll surveyed 2500 people nationwide from September 15 to 21. It did not provide a margin of error.

Thailand's current ruling coalition's leader, Prayuth Chan-ocha, polled fourth with 10.1 per cent.

Prayuth is currently suspended pending a court ruling in a case saying his time as a military junta leader starting in 2014 should count toward term limits.

He continues to work as defence minister and the Constitutional Court is expected to rule in the case on September 30.

Since populist leader Thaksin was ousted by the military in 2006, parties loyal to his movement have won successive elections but their prime ministers have been removed by court rulings and coups.

Prayuth first came to power in 2014 when as army chief he ousted an elected government that had been led by Thaksin's sister, Yingluck Shinawatra.

Paetongtarn Shinawatra, known by the nickname "Ung Ing", is an executive in the pro-Thaksin Pheu Thai party and began appearing at party rallies earlier this year.

Pheu Thai topped the opinion poll as the favourite party of 34.4 per cent of respondents, followed by "no party" at 24 per cent and the youth-oriented opposition Move Forward party with 13.6 per cent.

Prayuth's Palang Pracharat party was fifth with 5.6 per cent of respondents.

Australian Associated Press