Both parties are pinning their hopes on the polls to refurbish their image and shore up voter confidence that has been eroded by a massive corruption scandal involving former conservative President Park Geun-hye, observers said.

The new leaders will be tasked with preparing the parties for the gubernatorial and mayoral elections, slated for June next year, which are likely to be a referendum on the Moon Jae-in government's job performance.

The LKP leadership race has been shaping up to be a three-way match among former South Gyeongsang Province Gov. Hong Joon-pyo, five-term lawmaker Won Yoo-chul and four-term legislator Shin Sang-jin.

Hong, a brash-talking prosecutor-turned-politician, is the highest profile among the candidates as he ran in the May 9 presidential election and came in second with 24 percent of the vote.

Hong vowed to build a "powerful" opposition party to better keep the liberal ruling bloc in check.

"The LKP must be reborn as a powerful opposition force to reclaim an (ideological) balance in South Korea's society," Hong told Yonhap News Agency over the phone.

While throwing his hat in the ring Thursday, Won vowed to make a "young, healthy and open" party in a complete break from "factionalism and political hegemonism." Shin, for his part, pledged to rebuild a "wholesome rightwing party," representing new conservative values that genuinely serve citizens.

The LKP has decided to pick its new leader based on a vote by party delegates and a public opinion poll, which are weighted 70 percent and 30 percent, respectively.

The Bareun Party's race is more crowded. It features three-term lawmakers Kim Young-woo and Lee Hye-hoon, two-term Rep. Ha Tae-kyeung, and first-term legislators Jeong Woon-chun and Ji Sang-wuk.

The party was formed in January after its members defected from the then Saenuri Party, a precursor to the LKP amid a factional rift between them and those loyal to the ousted former president.

After six rounds of policy debates that begin Saturday, the party will pick its new chief based on a vote by party members and an opinion poll that are weighted 70 percent and 30 percent, respectively. (Yonhap)