A former minister ousted in Thailand's 2014 military coup was projected to win by a landslide in Bangkok's first election for governor in almost a decade on Sunday.

Around four million people were eligible to vote in the first major poll since the country was rocked by huge youth-led protests in 2020 demanding reform to the once-untouchable monarchy.

But daily life rather than politics dominated campaigning in the Thai capital, with candidates promising to clear up the congested, polluted and noisy megapolis home to 10 million.

"I am ready to be governor for everyone," independent frontrunner Chadchart Sittipunt said late Sunday, while emphasising he would wait for the final result from the electoral commission before declaring victory.

Local media reported that counting so far put the former transport minister in the lead with 1.2 million votes with 90 percent of ballots counted, following a turnout of roughly 60 percent.

"It does not matter if you voted for me or not, I have to serve everyone," Chadchart told supporters.

During his campaign the 55-year-old promised to tackle the capital's notorious traffic and made numerous green pledges while insisting voters wanted a change from entrenched political divisions.

Political analyst Napisa Waitoolkiat at Naresuan University's faculty of social sciences said Chadchart's success signalled young people and the middle class were "fed up".

Independent candidate Chadchart Sittipunt (L) casts his vote in Bangkok's governor elections after arriving at the polling station on his bike Independent candidate Chadchart Sittipunt (L) casts his vote in Bangkok's governor elections after arriving at the polling station on his bike Photo: AFP / Jack TAYLOR

"This is a message from Bangkokians, and particularly the new generation. They want a new leader who can revamp and change Bangkok," she said.

A record 30 candidates ran for the top job, eight years after a coup saw local elections scrapped and the city run by government-appointed leaders.

By Sunday evening, all of the leading candidates had conceded defeat to Chadchart.

Incumbent Aswin Kwanmuang, a former police general backed by Prime Minister Prayut Chan-O-Cha, said he would "accept what the people decide".

Left-wing candidate Wiroj Lakkhanaadisorn, of the Move Forward party, said he believed Chadchart had won.

"It shows that the public are not happy with the government's performance," he told Thai broadcaster Channel 3.

Polling centres opened across the city at 8 am (0100 GMT) and closed at 5 pm with temperature checks and Covid-19 restrictions in place.

The winner will be formally announced in the coming days, as the results must be ratified by the electoral commission.