Seoul, South Korea - South Korean lawmakers on Saturday impeached President Yoon Suk Yeol over his failed martial law bid, with the opposition declaring a "victory of the people."

The vote took place as hundreds of thousands took to the streets of Seoul in rival rallies for and against Yoon, who launched a failed attempt to impose martial law on December 3.

Out of 300 lawmakers, 204 voted to impeach the president on allegations of insurrection while 85 voted against. Three abstained, with eight votes nullified.

With the impeachment, Yoon has been suspended from office while South Korea's Constitutional Court deliberates on the vote.

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Prime Minister Han Duck-soo is now the nation's interim leader.

The court now has 180 days to rule on Yoon's future.

Two hundred votes were needed for the impeachment to pass, and opposition lawmakers needed to convince at least eight parliamentarians from Yoon's conservative People Power Party (PPP) to switch sides.

"Today's impeachment is the great victory of the people," opposition Democratic Party floor leader Park Chan-dae said following the vote.

A Seoul police official told AFP at least 200,000 people had massed outside parliament in support of removing the president.

On the other side of Seoul near Gwanghwamun square, police estimated 30,000 had rallied in support of Yoon, blasting patriotic songs and waving South Korean and American flags.

"Yoon had no choice but to declare martial law. I approve of every decision he has made as president," supporter Choi Hee-sun (62) told AFP before the vote.

The South Korean president has vowed to fight on and doubled down on unsubstantiated claims the opposition is in league with North Korea.

The main opposition Democratic Party said on Saturday said ahead of the vote that impeachment was the "only way" to "safeguard the Constitution, the rule of law, democracy and South Korea's future."

"We can no longer endure Yoon's madness," spokesperson Hwang Jung-a said.

At the rally outside parliament supporting impeachment, volunteers gave out free hand warmers on Saturday morning to fight the sub-zero temperatures, as well as coffee and food.

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K-pop singer Yuri of the band Girl's Generation – whose song Into the New World has become a protest anthem – said she had pre-paid for food for fans attending the demonstration.

"Stay safe and take care of your health!" she said on a superfan chat platform.

One protester said she had rented a bus so parents at the rally would have a place to change diapers and feed their babies.

Another said they had initially planned to spend their Saturday hiking.

"But I came here instead to support my fellow citizens," Kim Deuk-yun (58) told AFP.

If the Constitutional Court backs his removal, Yoon would become the second president in South Korean history to be successfully impeached.

But there is also precedent for the court to block impeachment. In 2004, then-president Roh Moo-hyun was removed by parliament for alleged election law violations and incompetence, but the Constitutional Court later reinstated him.

The court currently only has six judges, meaning their decision must be unanimous.

Yoon has remained unapologetic and defiant as the fallout from his disastrous martial law declaration has deepened and an investigation into his inner circle has widened.

His approval rating – never very high – has plummeted to 11%, according to a Gallup Korea poll released Friday.

The same poll showed that 75% now support his impeachment.