Thailand's King Maha Vajiralongkorn has endorsed a decree to dissolve parliament, the Royal Gazette has announced, paving the way for elections. An election must be held 45 to 60 days after the house dissolution, which takes effect immediately. Prime Minister Prayut Chan-o-cha has been in power since a 2014 coup against the Pheu Thai government. "This is a return of political decision-making power to the people swiftly to continue democratic government with the King as head of state," the decree published on Monday said. 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 was dissolved on Monday. Thailand's election is expected to showcase a long-running political battle between the billionaire Shinawatra family and the country's conservative 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 polls, with her support jumping 10 points to 38.2 per cent in a survey released at the weekend. The poll by the National Institute of Development Administration (NIDA) put incumbent Prayut in third place with 15.65 per cent. 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. Australian Associated Press