Oh Se-hoon of the main opposition People Power Party (PPP) is expected to win the Seoul mayoral seat by a solid margin in Wednesday's by-elections, Yonhap reported, citing an exit poll.

The by-elections are seen as a major bellwether for next year's presidential election. The upcoming South Korean presidential election is expected to be held in March 2022.

Oh defeated his rival from the ruling Democratic Party (DP) Park Young-sun 59 percent to 37.7 percent in the exit poll, jointly released by three broadcasters: KBS, MBC and SBS.

The Seoul mayoral by-election was called after the previous mayor, Park Won-soon affiliated with the DP, apparently took his own life in July last year in the face of sexual harassment allegations raised by a female subordinate.

The joint exit poll also showed Park Heong-joon of the PPP leading DP rival Kim Young-choon 64 percent to 33 percent in the race for the mayoralty of Busan, the country's second-largest city.

Besides the two mayoral positions, 19 other regional public posts are also up for grabs in the by-elections.

If elected, Oh will return to the mayoral seat of Seoul. He left the post at the midpoint of his second term in 2011, in protest against the opposition-dominated city council's introduction of a free school lunch program for all students. 

(Cover: Oh Se-hoon celebrates the result of an exit poll at the headquarters of the main opposition People Power Party in Seoul on April 7, 2021. /Yonhap)