Seoul (AFP) - Lawmakers camping out in parliament, hundreds of thousands of protestors expected outside, a landmark vote to impeach the president over martial law – South Korean democracy faces its “most critical moment”, opposition leader Lee Jae-myung told AFP Friday.

The country could have a new interim leader as soon as Saturday night, if the impeachment motion set for 7 pm (1000 GMT) succeeds in removing wildly unpopular President Yoon Suk Yeol from office over his bid to impose martial law on the democratic South.

Until Yoon is impeached, there remains a risk he may try to subvert civilian rule again, Lee said, warning that the country in turmoil was vulnerable to “another martial law attempt”.

“With the impeachment vote set for tomorrow, the hours leading up to it are extremely precarious,” Lee told AFP at the National Assembly, where he and his party’s lawmakers have been camped out for days, sleeping in their offices and not daring to leave the compound.

“Tonight will be the most critical moment” Lee said, with his MPs planning to all sleep in the main debating chamber, with buses parked on the lawn outside to block helicopters from landing, as happened on Tuesday night.

“People might believe the military and police would hesitate to support a second attempt, but Yoon could exploit loopholes to give it another try,” Lee said.

Lee’s Democratic Party, which holds a majority in the 300-member parliament, has instructed all of its 170 lawmakers to stay inside the main building until the impeachment vote.

This unprecedented “sleep-in” follows revelations that the soldiers who stormed the National Assembly Tuesday had orders to arrest and detain lawmakers, including Lee, top army officials have said.

One of the key reasons the “absurd and dangerous coup” attempt failed, Lee said, was because of the bravery of ordinary South Koreans.

It was “thanks to citizens who blocked armoured vehicles by sitting in the streets and to parliamentary staff and lawmakers who put their lives on the line,” he said, using office furniture to fend off heavily armed troops and giving MPs enough time to vote.

- ‘Race against time’ -

Lee, who narrowly lost to Yoon in the 2022 presidential election, has been warning for months that Yoon might resort to martial law – a claim critics dismissed as “ridiculous fear-mongering”.

Lee was ready for bed Tuesday night, when his wife rushed in showing him a video of President Yoon announcing martial law – at first, the veteran leader assumed it must be a deepfake.

“When my wife told me Yoon had declared martial law, I told her to stop joking,” he said.

But once he grasped the seriousness of the situation, he immediately messaged his party’s lawmakers, telling them to get to the National Assembly, then jumping in his car – his wife drove – and livestreaming on his YouTube to call for help.

“President Yoon’s illegal martial law declaration is invalid. Please come to the National Assembly now. I am heading there as well,” he urged supporters from the car.

Soon, thousands of people had gathered outside the parliament building, chanting: “Arrest Yoon!”

“With parliamentary staff physically blocking the soldiers, we managed to pass a resolution just a step ahead of them (soldiers)…. It was a race against time,” he said.

- Growing guilt -

Lee urged Yoon to step down, saying that he could yet bring “the unfortunate situation to an end” before the vote and, if it succeeds, a court ruling that would finalise it.

“Every minute he stays in office, his guilt and responsibility grow larger,” he said.

South Korea has risen from colonialism and war to become Asia’s fourth-largest economy and a vibrant democracy, with its cultural power – from K-pop to a Nobel-prize-winning author – soaring globally.

Lee insisted this week’s six-hour stint of martial law – the first in over four decades – should be viewed as an isolated misstep.

“It’s vital to view Yoon’s highly irrational, impulsive, and unreasonable decision as an extraordinary anomaly,” he said.

He compared it to “a sudden fever caused by bacteria” that the body’s immune system quickly overcomes.

“South Korea’s democracy is strong, and its people are courageous and wise. That is why this absurd attempt at a military coup was defeated so swiftly.”

Passing the impeachment motion will require eight lawmakers from Yoon’s ruling party to vote with the opposition – and Lee said although he was increasingly confident they could do it, he did not know for sure.

He urged ruling party lawmakers to “reflect on what politics truly is. It is about representing the will of the people… and the people’s will is now clear”.