Rival parties made last-minute efforts to win over voters on Tuesday, one day before by-elections to pick two lawmakers and three local councilors.

The size of the by-elections is small, but political parties see the votes as a litmus test ahead of the nationwide parliamentary elections slated for April 2020.

The main focus will be two parliamentary seats up for grabs in South Gyeongsang Province located in the country's southeastern region.

The constituencies at stake lie in Changwon, 400 kilometers southeast of Seoul, and Tongyeong-Goseong, 450 kilometers southeast of the capital.

Key party officials flocked to the province to help their candidates attract voters on the final day of campaigning.

Liberal politicians have received strong voter support in the industrial city of Changwon. Except for in 2012, three liberal candidates have been selected in general elections since 2004.

Conservative contenders have held firm in Tongyeong on the southeast coast.

The province, the manufacturing hub for the country's auto and shipbuilding industries, is bearing the brunt of the economic downturn. Rival parties have unveiled pledges to prop up the regional economy to appeal to voters.

Last week, the ruling Democratic Party (DP) and the leftist Justice Party filed a single candidacy in an effort to muster liberal votes.

Yeo Young-guk of the minor party will run in the Changwon district. The parliamentary seat has been vacant following the suicide of progressive lawmaker Roh Hoe-chan of the Justice Party.

His rival is Kang Gi-yun of the main opposition Liberty Korea Party (LKP), a former lawmaker.

Kang has told conservative voters that the liberal government's nuclear-free policy dented the regional economy in Changwon, where nuclear energy-related firms are clustered, his team said.

Following the merger of the candidacies, the ruling DP has lent its support to Yeo.

"We are appealing for votes, highlighting concerns that the split of liberal votes will help the LKP candidate win in a region where progressive politicians usually stood out," said an official on Yeo's election team.

The minor opposition Bareunmirae Party raised the need to shake off liberal and conservative ideological divides that it claimed dented the growth of the regional economy.

Wednesday's voting will kick off at 6 a.m. and is to run until 8 p.m.

The turnout for early voting held on Friday and Saturday reached 14.37 percent, with the turnout for just the parliamentary by-elections coming in at 14.71 percent. (Yonhap)