A woman casts her ballot during advance voting at a polling station in Bangkok ahead of the May 14 general election
A woman casts her ballot during advance voting at a polling station in Bangkok ahead of the May 14 general election AFP

Thais queued under the blistering sun outside temples, shopping centres and schools to cast their early ballots Sunday ahead of a much-anticipated election next week.

More than two million Thais nationwide are registered to vote early ahead of the kingdom's May 14 election, which is shaping up to be a clash between army-backed establishment parties and resurgent opposition movements.

Prime Minister Prayut Chan-o-Cha, who took power in a 2014 coup before cementing control in a controversial 2019 election, has been languishing in opinion polls with voters favouring old-school opposition party Pheu Thai and the more radical Move Forward Party.

But with an electoral system heavily stacked in favour of the army-backed parties, challengers must achieve a landslide victory to have any hope of forming the next government.

"I hope this election will change the country in a better way," said shopping mall worker Srisuda Wongsa-ad, 28, after casting her ballot.

She was among hundreds queuing quietly at a polling station in Bangkok's fashionable Ekkamai district to vote at the Wat That Thong.

"I am voting for a candidate and party that I like, that can answer my needs," she said.

Elsewhere in the capital, the Royal Paragon Hall shopping centre was packed with voters, albeit cooler ones, enjoying the complex's air conditioning.

Temperatures across the capital soared as the day went on, with machines spraying a fine mist of water over orderly queues at the busy Ramkhamhaeng University polling station shortly before midday.

But crowds were still out in force, with traffic and congestion around busy polling stations.

"I am quite excited," said first-time voter Pasawee Sriarunothai, 20, who will not be in Bangkok on May 14.

"I decide to cast my vote based on the party's policies, and I hope this election will bring the country a better future," Pasawee said.

"I want the new generation to be running the country. I want to try something new," said Nantthapon Phomput, 28, before voting at Wat That Thong.

Among the challengers are opposition party Pheu Thai, fielding Paetongtarn Shinawatra -- daughter of billionaire ex-premier Thaksin Shinawatra -- as a prime ministerial candidate.

While Pheu Thai remains in the lead, Paetongtarn was overtaken as surveyed voters' preferred PM candidate by Pita Limjaroenrat, leader of the rival opposition Move Forward party.

Following polls closing at 5:00 pm (1000 GMT), Electoral Commission secretary general Sawaeng Boonmee said turnout was estimated at around 70 percent, although he stressed the need to wait for an official count.

Authorities had anticipated large numbers of early voters.

An additional 100,000 Thais living overseas will also vote early, with some having already done so.

More than 52 million citizens are eligible to vote in this election.