Polls opened Wednesday for the first by-elections to be held under the new government of President Park Geun-hye, in what is seen as a crucial test of public support for the administration.

Voting began at 6 a.m. at 283 polling stations in the 12 electoral districts nationwide and is to run until 8 p.m. At stake are three parliamentary seats and nine posts in local governments and councils.

The focal point of attention is the possible comeback of former presidential candidate Ahn Cheol-soo, who is running as an independent for a parliamentary seat in Seoul's Nowon C district.

Ahn, the founder of South Korea's largest anti-virus software firm AhnLab, demonstrated huge political influence among young and liberal voters ahead of last year's presidential race, although he eventually dropped out to help boost the chances of the main opposition candidate, Moon Jae-in.

As the current front-runner in his district, the independent has maintained a lead over the ruling Saenuri Party candidate, Huh Joon-young, in the absence of a rival from the main opposition Democratic United Party (DUP).

The DUP did not field a candidate in what was seen as repayment for Ahn's withdrawal from last year's presidential race.

However, political experts warned that the results could depend on the final turnout. In South Korea, a low turnout has often worked in favor of the conservative ruling party, whose supporters are generally older and more likely to vote.

A high turnout usually indicates that more young and liberal voters went to the polls in support of the opposition.

Some expect a turnout as high as 40 percent due in part to the fact that voters had a chance to cast their ballots during the two-day early voting period that ended Saturday. It was the first time that the early voting system, adopted under a revised law in February 2012, had been used.

The average voter turnout during that period was 4.78 percent, while the voting rate for the three parliamentary seats was tallied at 6.93 percent. In last year's general elections, the average absentee voting turnout for the three districts stood at 1.94 percent.

The two other parliamentary seats on offer are in Yeongdo in the southeastern port city of Busan and in the Buyeo and Cheongyang constituency in South Chungcheong Province.

The ruling party's candidates have held a strong lead over their rivals in both districts, according to public opinion surveys. (Yonhap News)