The lyrics of "Into the New World," Girls' Generation's 2007 debut single, echoed through the streets of Yeouido on Saturday evening: "Our rough road is before our eyes. Unknown future and walls. I won't change, I'm not giving up."

What could have been a scene from a K-pop concert was, in fact, a massive demonstration being held in response to an unthinkable development in South Korean democracy: a president's shock declaration of martial law.

The streets of Yeouido were filled with citizens — about 150,000 according to police estimates — who gathered outside the National Assembly throughout Saturday to make their voices heard as lawmakers gathered to vote on Yoon's impeachment.

The impeachment motion against Yoon collapsed that night after ruling party lawmakers walked out en masse and a quorum of 200 lawmakers could not be reached.

A nation holds its breath

Throughout Saturday, anticipation and suspense ran high across the country. Even typically apolitical citizens were glued to news coverage as behind-the-scenes negotiations intensified.

"I've been wired into news and YouTube to follow politics lately, could barely wind down after work," said Kim, 57, an orthodontist from Bundang, south of Seoul.

A self-described centrist typically indifferent to politics, she found herself totally outraged by the latest political drama.

"What's driving me nuts more than the martial law declaration itself is the ruling party's rallying around the president to block his removal. It's all just a huge circus."

Polling released Thursday morning, two days after the martial law declaration on Tuesday night, showed nearly three in four registered voters supported impeachment. However, some expressed reservations about opposition control.

"The whole impeachment process seems rushed," said a 29-year-old engineer who gave only his English name, Tony. "We should wait for investigation results to evaluate the constitutionality of martial law," he said.

Streets fill with protesters

By early afternoon, tens of thousands of protesters had transformed Yeouido, Seoul's financial hub and home to the National Assembly, into a sea of demonstrations.

The December wind cut sharp off the Han River, with temperatures hovering near freezing. People from all walks of life, including workers, students and religious figures, stood shoulder to shoulder, bundled in thick winter coats while holding signs demanding Yoon's removal. The crowd grew so large that subway operators bypassed two nearby stations.

The protesters pulled no punches in expressing their fury.

"This man was riddled with scandals even before this incident, including those surrounding the first lady. I can't wait for the impeachment to pass," said a 35-year-old office worker who had traveled from Eunpyeong-gu in northern Seoul to "show the power of the people."

The sounds of chants shook through Yeouido as police closed off major thoroughfares leading to the National Assembly building. A constant flow of people flooded through the dense crowd, carrying signs past stages set up for speeches and performances. By 4 p.m., the area was so packed that reporters struggled to transmit coverage due to overwhelmed cell networks.

Meanwhile, in a stark display of the nation's political divide, some 20,000 people, according to police estimates, were gathered in central Seoul's Gwanghwamun Square, waving Korean and American flags while calling for opposition leader Lee Jae-myung's arrest.

They displayed banners reading "Protect our President" and "Arrest Lee Jae-myung for treason," accusing the opposition of orchestrating a scheme to destabilize the government.

"I'm here to protect the country and our democracy," said an elderly demonstrator clutching a Korean flag. "President Yoon has done so much good for our country, but the left-wing media won't report any of it. That's what makes my blood boil," she added.

Hope fades but resolve strengthens

The mood at Yeouido shifted when ruling party members began exiting the National Assembly hall en masse at 6:30 p.m., making the impeachment vote's failure all but inevitable. But even as night fell and temperatures dropped further, the crowd only continued to swell.

"I feel totally disregarded," said a man in his 50s from Seoul, his voice rising with anger. "It’s as if they're saying, 'OK there are a million of you on the streets, so what?'"

Thousands remained firmly planted on the street, their chants of "Impeach Yoon Seok Yeol" and "People Power Party come back" echoing through the area. As some protesters marched toward the National Assembly building, others lit candles, in a reminder of the peaceful 2016 demonstrations that ultimately led to former President Park's removal from office.

"It was more or less expected," said another Seoul resident in his 50s, noting the earlier meeting between the ruling party leader Han Dong-hoon and Prime Minister Han Duck-soo. "We shouldn't forget what the president has done. We don't know what he's going to do next."

The sound of Girls' Generation's "Into the New World" filled the air again, its lyrics taking on new meaning with the moment. The song, a protest anthem for some time, was followed by other K-pop hits like G-Dragon's "Crooked" and aespa's "Supernova." Protesters wielding glow sticks — a staple of K-pop concerts now repurposed for political expression — swayed in unison as they chanted along to the songs' infectious melodies.

"This is just the beginning," declared one protester, raising the glow stick as he vowed to stay until midnight. "We will continue to act collectively."

Foreign residents react

As countless South Koreans took to the streets, foreign residents in the country watched the drama unfold with a mix of concern and wonder.

"I'm just curious to see how it impacts our life here in Korea, especially as someone who's purely here on a visa," said an American resident in her 30s who requested anonymity.

"It's surprising that they are not sticking to what they had mentioned earlier in the same day," she said, referring to initial promises from some ruling party lawmakers to support impeachment.

A longtime resident from Europe urged calm amid the turmoil.

"The last time Koreans ousted President Park Geun-hye, Korea was praised around the world for the democratic and peaceful process," he said. "It's extremely important that things remain that way."

For Jasmine Lee, who was the first foreign-born lawmaker in Korea's history, the events stirred powerful memories.

Growing up in the Philippines, the 47-year-old witnessed the 1986 People Power Revolution -- a sustained campaign of civil resistance that peacefully ended Ferdinand Marcos's 20-year dictatorship. Later, as a member of Korea's National Assembly from 2012 to 2016, she watched as millions of candlelight protesters successfully pushed for President Park Geun-hye's impeachment.

Expressing initial shock at the martial law declaration, Lee said she had fully expected Saturday's massive turnout at the National Assembly.

"This is a country that came back from the ashes, that has prided itself on how democracy helped Korea become what it is today," she said. "Whatever happens with this particular impeachment motion, people will stand up."

"If it's not the politicians who are going to do this, it's the people who will make it happen."

The words seemed to carry across Yeouido's streets, where protesters continued singing into the night, their voices merging with the winter wind off the Han River.

The Korea Herald intern Kwon Min-seo contributed to this report.