South Korea's Democratic Party's presidential election candidate Lee Jae-myung is the frontrunner for the upcoming June 3 election
South Korea's Democratic Party's presidential election candidate Lee Jae-myung is the frontrunner for the upcoming June 3 election AFP

The candidates vying to lead South Korea kicked off their official campaigns Monday ahead of a snap presidential election to replace the country's impeached ex-leader, removed over a thwarted martial law bid.

On June 3, South Korean voters will pick a new president, offering closure after months of political turmoil triggered by Yoon Suk Yeol's ill-fated effort to suspend civilian rule in December.

For 22 days from Monday, the six officially registered presidential candidates will campaign across the country, accompanied by ear-splitting blasts of re-written K-pop songs, with uniformed campaign staff performing choreographed dance moves.

The frontrunner by a large margin, polls show, is main opposition Democratic Party candidate Lee Jae-myung, with 43 percent support.

Hundreds of supporters gathered in central Seoul early Monday chanting "Lee Jae-myung, President!" as Lee officially kicked off his campaign.

Lee, who narrowly lost in 2022 presidential elections to Yoon, thanked all his supporters who "helped rebuild after the painful defeat".

"I promise to repay their support with victory," he told a cheering crowd.

After a chaotic few days of party infighting, the country's conservative People Power Party (PPP) said Sunday that former labour minister Kim Moon-soo would be their official candidate.

Kim, who is polling at around 29 percent support according to most recent data, started his official campaign at a local market in Seoul.

"I genuinely believe I must become a president for the people: a president for livelihoods, a president for the economy," Kim told reporters on Monday morning.

"I must be a president who ensures the people of South Korea live well."

Kim was picked by the party on May 3, only to have his nomination cancelled a week later as party bigwigs sought to replace him with ex-prime minister Han Duck-soo, who was seen as a stronger bet.

However, the party's rank and file voted down the motion, meaning Kim was reinstated as the nominee by Saturday night.

The turmoil has experts and PPP supporters warning that unless they get their act together, it will be an easy victory for Lee in the upcoming elections.

"The PPP is just a mess. They are just self-destructing," Lee Jung-ja, a 52-year-old self-described PPP voter told AFP, as he watched Lee kick off his campaign in downtown Seoul.

"Even if they unite, it still won't be enough. All they're doing is fighting with each other. I bet Lee Jae-myung is gloating."

Experts believe the conservatives' internal chaos has weakened their chances in the election, a contest where they were already at a significant disadvantage.

"The upcoming election is likely to become a battle between Lee Jae-myung and those opposing him," said Kang Won-taek, a political science professor at Seoul National University.

"The problem, however, is that the opposing side, specifically the conservative camp, seems to be greatly divided."

The fact that both the last PPP presidents -- Park Geun-hye and most recently Yoon -- were impeached "reflects a broader crisis" in the party, Kang said.

The upcoming election may show that the conservative party "no longer seems sustainable in its current form".