The by-election for the chief of Seoul's key district kicked off Wednesday, with the result expected to serve as a key barometer of voter sentiment ahead of the parliamentary elections slated for April next year.

Eligible voters in Gangseo Ward started casting their ballots at polling stations from 6 a.m, according to the National Election Commission. The voting is to run until 8:00 p.m.

Although the election picks one of Seoul's 25 ward chiefs, the election has gained much attention, with the turnout for the two-day advance voting recording the highest ever in the country's by-election history.

During the early voting on Friday and Saturday, 113,313 out of the total 500,603 eligible voters cast their ballots, representing a turnout of 22.64 percent, the NEC said.

The by-election takes place after former ward chief Kim Tae-woo was removed from the post in May due to a suspended prison sentence for leaking secrets he gained while working for a special inspection team under former President Moon Jae-in.

Although the seat was vacated due to Kim's conviction, the ruling People Power Party has named him as its candidate after his right to run in the election was reinstated following a special presidential pardon in August.

Kim's rival of he main opposition Democratic Party is Jin Kyo-hoon, a former deputy chief of the national police.

A total of six candidates are running in the by-election, including Kim and Jin. (Yonhap)