Thailand's King Maha Vajiralongkorn has endorsed a decree to dissolve parliament, according to an announcement in the Royal Gazette on Monday, paving the way for elections in May.

An election must be held 45 to 60 days after the house dissolution, which takes effect immediately.

"This is a return of political decision-making power to the people swiftly to continue democratic government with the King as head of state," said the decree published on Monday.

An election date has yet to be announced but Deputy Prime Minster Wissanu Krea-ngam earlier in the day said it would likely be held on May 14, if the house were dissolved on Monday.

Thailand's election is expected to showcase a long-running political battle between the billionaire Shinawatra family and the country's pro-military establishment.

Paetongtarn Shinawatra, the daughter and niece respectively of ousted former premiers Thaksin and Yingluck Shinawatra, is the frontrunner to be prime minister in opinion surveys, with her support jumping 10 points to 38.2 percent in a poll released at the weekend.

The poll by the National Institute of Development Administration put Prime Minister Prayuth Chan-ocha, who has been in power since a 2014 coup against the Pheu Thai government, in third place with 15.65 percent.

Prayuth is polling behind the pro-reform Move Forward Party, which hopes to capitalise on the anti-establishment spirit of the 2020 street protests.

The election is the second since the 2014 coup and the first since the country was rocked by the 2020 protests.

Chulalongkorn University political analyst Thitinan Pongsudhirak said the election would be "most consequential in my lifetime".

It will decide whether the kingdom "breaks out of an entrenched prolonged rut that goes back two decades", he said.

Paetongtarn on Friday said she was confident of winning the election by a landslide, with the aim of averting any political manoeuvring against her party, which has previously been removed from office by judicial rulings and military coups. (AFP/Reuters)