Bangkokians were advised to cast their ballots early on Sunday, with the likelihood of rain in the afternoon, as polling opened in the election of a new city governor and city council.
Polling booths opened at 8am and voters have until 5pm to cast their ballots.
The unofficial results are expected by 10pm.
About 74,000 staff were deployed at 6,628 polling stations across the capital. The poll organising office expected 70% of more than 4 million registered voters to turn out.
City clerk Narong Ruangsri, the Bangkok election director, said on Sunday all preparations went smoothly and advised voters to come out before anticipated rain in the afternoon.
"Voters should show up before the afternoon. If you plan on afternoon voting, please bring an umbrella because it could rain," Mr Narong said during a media briefing.
Election Commission chairman Narong Klanwarin said rain would not delay counting of votes after the polls close and expected the unofficial results by 10pm, as earlier planned.
The Bangkok Metropolitan Administration said there was a 60% chance of rain from 4pm, possibly in northern districts and part of the eastern suburbs including Don Muang and Bang Khen.
