Polls opened Wednesday for small yet significant parliamentary and local by-elections seen as a test for the rival parties and some of the potential presidential candidates before South Korea elects a new parliament and a new president next year.

Three parliamentary seats and one gubernatorial post are on offer in the elections, with the other 34 races vying for small local government heads and council members. The results do not affect the overall make-up of the 299-member National Assembly where the ruling Grand National Party (GNP) has a majority.

Still, the elections are considered important for the ruling GNP, the main opposition Democratic Party, and some potential presidential hopefuls because a poor showing for either party could ultimately lead to its leadership change and the outcome could also affect chances of presidential aspirants.

The election, aimed at filling posts vacated due to convictions of corruption and other reasons, effectively comes down to three key races -- two for parliamentary seats representing a district in Bundang, south of Seoul, and Gimhae, South Gyeongsang Province, and the other for governorship of Gangwon Province.

The GNP, which holds a majority in the unicameral parliament with 171 seats, did not field any candidates for a parliamentary district in the opposition stronghold of Suncheon, South Jeolla Province, because it sees no chances of winning the race.

Political watchers say winning two of the three key races will mean a victory for the ruling party, while a defeat in its traditional stronghold Bundang will deal a blow to the party and could spark calls for a leadership change.

The race in Bundang is considered the biggest match of Wednesday's elections as Sohn Hak-kyu, current leader of the main opposition DP, runs in the traditional GNP stronghold against the former GNP chief, Kang Jae-sup, a five-term lawmaker.

A victory for Sohn would be a boon for his presidential ambitions, while a defeat would be a critical blow. The opposition leader, who defected from the ruling GNP four years ago, has said he staked his political career on Wednesday's election.

Campaign watchers have not been able to make predictions in the district because the race has been too tight. Early polls showed that Kang and Sohn were running neck-and-neck within the margin of error of four percentage points.

In Gimhae in South Gyeongsang Province, the hometown of late former President Roh Moo-hyun, the unified candidate from the loosely formed opposition coalition, Lee Bong-soo of the People's Participatory Party (PPP), is facing Kim Tae-ho of the GNP.

Kim has made all-out efforts to restore his tarnished image after stepping down from a nomination for prime minister last year over his alleged connection to a scandal-ridden businessman during a parliamentary confirmation hearing.

A victory for Kim would give him momentum to make a successful comeback because he would be credited with winning in an unfavorable district where many voters are still believed to be feeling nostalgic for Roh, who committed suicide in 2009 amid a prosecution probe into alleged corruption involving his family.

If Lee of the fledgling minor opposition PPP, which has no parliamentary seat, wins the race, it would give its party leader and presidential hopeful Rhyu Si-min the chance to show his strength in the opposition bloc for his contribution to the election.

In Gangwon Province, rival candidates with similar backgrounds-- both of whom were born in the province and served as presidents of broadcaster MBC before entering politics -- are vying for governorship that has remained empty since Lee Kwang-jae of the DP lost his seat following a bribery conviction. 

In February, Choi Moon-soon stepped down from the DP's proportional representation seat to run in the election, while it is the first political battle for Ohm Ki-young of the GNP after ending his journalism career last year.

Voting began at 6 a.m. and will continue till 8 p.m., according to the National Election Commission (NEC), and forecasts of preliminary results will become available before midnight.

(Yonhap news)