Supporters of President Yoon Suk Yeol rally at Seoul's Gwanghwamun area on Saturday. (Yonhap)

When a speaker holding the microphone said, "This is invalid! President Yoon Suk Yeol, stay strong. We will surely protect you, Mr. President!" the crowd of some 40,000 Yoon supporters gathered at Gwanghwamun erupted in cheers. They shouted that they would gather next week as well.

This came moments after the impeachment motion against Yoon passed with a vote of 204 in favor, 85 against, 3 abstentions and 8 invalid votes. The country’s Constitutional Court will now deliberate on the motion, a process that could take up to 180 days. Prime Minister Han Duck-soo will serve as acting President during the court’s deliberation.

“I’m very upset. It’s frustrating to see people being swayed like this, especially after everything that happened during Park Geun-hye’s time,” said a 33-year-old man from Busan.

Another man in his 50s from Gyeonggi Province said, “The case will be dismissed. It’s a sad day, but the Democratic Party will not be able to present any legal grounds. Martial law is not illegal.”

“A sense of community has collapsed. The nation’s order is falling apart. This vote is invalid,” said a 65-year-old woman who had traveled from Incheon, Gyeonggi Province. “The President is no fool. He has a plan.”

Supporters of President Yoon Suk Yeol rally at Seoul's Gwanghwamun area on Saturday. (Yonhap)

While tens of thousands of people gathered in the streets outside the National Assembly in Yeouido to call for Yoon’s impeachment, a counter-protest unfolded in the Gwanghwamun area in downtown Seoul where demonstrators opposed the impeachment and demanded the arrest of opposition leader Lee Jae-myung.

The rally was primarily organized by Rebuild Korea (Daegukbon), a far-right civic group, and the Liberty Unification Party. Police unofficially estimated the crowd at 40,000.

By early afternoon, hours before the impeachment vote, a predominantly middle-aged and older crowd had formed a 1.5-kilometer-long line stretching from the statue of Admiral Yi Sun-sin to Sungnyemun Gate. They waved Korean flags, some carrying American flags as well, and held banners reading, “Against impeachment” and “Arrest Lee Jae-myung.”

Participants expressed anger at the impeachment motion, denouncing the opposition party and its leader Lee.

“I came because the situation is abnormal,” said a man in his 30s who traveled from Goyang, Gyeonggi Province. “(The opposition party) is attempting a legislative coup with over 23 impeachments and now shielding Lee. There are even talks of a ‘peaceful martial law.’ They are the real rebels.”

Another participant in his 60s, who came from Uijeongbu in Gyeonggi Province said, "It's heartbreaking that the president we voted for is facing this situation. How troubled must he have been to make such a move? He is still much better than Lee.”

“Declaring martial law was within the president’s authority,” said a man in his 60s who came from Daegu to defend Yoon’s actions.

Among the crowd was a Taiwanese tourist in her 40s, who observed, “It’s amazing that most people are elderly. I thought the Korean president would have been a strong supporter of democracy but was surprised by the martial law declaration. These things also happen in Taiwan, but the divide between young and old generations regarding political views is not as dramatic as here.”

Police buses are parked along Hannam-daero, blocking access to the presidential residence on Saturday afternoon. (Choi Si-young/The Korea Herald)

Things were quiet near the presidential residence in Hannam-dong, but tensions increased as the 202 Presidential Mobile Police Force blocked access to the area with police buses. They conducted spot checks, even on reporters, and cordoned off sidewalks along Hannam-daero in front of the president's official residence.

"Impeachment was just a matter of time," said a passerby in his 50s, surnamed Yeom. "I was shocked by (the military troops) breaking the windows of the National Assembly. It's a heartbreaking reality, but it seems things are quickly returning to normal. Today feels like a breath of fresh air amid these chaotic days."

Yoon has faced mounting criticism after a controversial declaration of martial law on Dec. 3, deploying military troops to the National Assembly, and refusing to step down despite strong backlash over the decision.

Instead, he criticized those who sought to remove him over his short-lived decision to impose military rule. Saturday’s impeachment vote follows the failure of the first impeachment motion on Dec. 7, due to a boycott of the vote by all but three ruling party lawmakers.

The Korea Herald reporters Kim Jae-heun, Choi Si-young and No Kyung-min contributed to this report.