With no clear winner in last month's local elections - which was President Park's first electoral test since taking office in February last year today's by-election is seen as a pivotal opportunity for both the ruling party and the main opposition to gain an upper hand.
Just two hours remain before polls close and our political correspondent Ji Myung-kil joins us live from the National Assembly.
So Myung-kil, what is the atmosphere there like?
Good evening, guys. Well, it was business as usual for the most part here at the National Assembly.
Both rival parties held their regular daily meetings here in the Assembly building today , but also took time to urge voters to cast ballots.
Early this morning, co-leader of the main opposition New Politics Alliance for Democracy, Kim Han-gil, attended a campaign event in front of a high school in the Gimpo district, urging people to vote.
The National Election Commission expects voter turnout to be around 30 percent when all is said and done.
A total of 15 parliamentary seats are up for grabs in this by-election, making it the largest in Korea's history.
At today's meetings the ruling Saenuri Party made pleas to the people, asking them to vote for their candidates so they can secure a stable majority in the National Assembly.
The New Politics Alliance for Democracy urged voters to send a warning to the incumbent government for its perceived poor handling of April's ferry tragedy.
The ruling party and the main opposition split municipal or local elections in early June and perhaps following up on that there are a number of very close races throughout the nation.
Are those races keeping the rival parties on the edge of their seats today?
Well, I would imagine so, Connyoung but really, at this point, there isn't much to do but to sit back and wait for those first results to come in.
The last opinion polling we had access to showed that each party had clear leads in three constituencies each.
That leaves uncertainty in the other nine races.
Last week's opinion polls showed neck-and-neck races in Seoul and its surrounding Gyeonggi-do province.
Both are considered barometers of public sentiment.
In Seoul's Dongjak-B district, former Saenuri Party lawmaker Na Kyung-won is running against Roh Hoe-chan of the minor opposition Justice Party.
Ki Dong-min of the main opposition party quit last week to to support Roh and to prevent splitting the liberal vote.
Another important district is the Suwon-C constituency in Gyeonggi-do province, where former opposition leader Sohn Hak-kyu is not only hoping to win a seat in the city of Suwon but also hoping to solidify his position within the opposition bloc.
He's up against the ruling party's Kim Yong-nam.
This is all I have for the moment.
I'll be back with a clearer picture of the election results in our later newscasts.
Back to you in the studio.