Pheu Thai's prime ministerial candidate, Paetongtarn Shinawatra, votes at a polling station in Bangkok on Sunday. Reuters

Vote counting started after polls closed, with the election commission expected to announce preliminary results by 10pm (1500 GMT). A live count by the poll body and a parallel unofficial count were already underway.

The election commission earlier projected a turnout of 80% of Thailand's 52 million eligible voters.

Voters got to choose among progressive opposition parties - one with a knack for winning elections - and ruling coalition parties allied with royalist generals keen to preserve the status quo after nine years of government led or backed by the army.

With votes counted from just over a quarter of polling stations, the reformist Move Forward Party (MFP) was on nearly two million votes, followed by Pheu Thai on 1.8 million, according to Election Commission figures.

The numbers are broadly in line with pre-election opinion polls, which forecast success for the opposition and heavy defeat for Prayut.

Pheu Thai is the latest iteration of the political movement founded by billionaire former premier Thaksin Shinawatra that has dominated Thai elections for two decades. But MFP has grown rapidly, fuelled by the youth-led protests that erupted across Bangkok in 2020 to demand democratic change and reform to Thailand's untouchable monarchy.

Prayut's United Thai Nation party lay in third place with around 700,000 votes.

Pheu Thai and MFP still face a battle to take power because the prime minister will be chosen not just by the 500 elected MPs but also by 250 senate members handpicked by the last military junta.

Thailand has seen a dozen coups since 1932 and there are fears an unclear or disputed result could lead to fresh military intervention or street protests.

Agencies