South Korea's opposition parties on Wednesday submitted a motion to impeach President Yoon Suk Yeol, who is facing pressure to leave office hours after he ended a short-lived martial law that prompted troops to encircle parliament before lawmakers voted to lift it.

Impeaching Yoon would require the support of two-thirds of parliament for the motion and then the backing of at least six Constitutional Court justices. The motion, submitted jointly by the main opposition Democratic Party and five smaller opposition parties, could be put to a vote as early as Friday.

Yoon's senior policy advisers and Defense Minster Kim Yong Hyun offered to resign, as the nation struggled to make sense of what appeared to be a poorly-thought-out stunt.

In the capital, tourists and residents walked around, traffic and construction were heard, and other than crowds of police holding shields, it seemed like a normal sunny, cold December morning.

On Tuesday night, Yoon abruptly imposed the emergency martial law, vowing to eliminate "anti-state" forces after he struggled to push forward his agenda in the opposition-dominated parliament. But his martial law was effective for only about six hours, as the National Assembly voted to overrule the president. The declaration was formally lifted around 4:30 a.m. during a Cabinet meeting.

The liberal opposition Democratic Party, which holds a majority in the 300-seat parliament, said Wednesday that its lawmakers decided to call on Yoon to quit immediately or they would take steps to impeach him.

"President Yoon Suk Yeol's martial law declaration was a clear violation of the constitution. It didn't abide by any requirements to declare it," the Democratic Party said in a statement. "His martial law declaration was originally invalid and a grave violation of the constitution. It was a grave act of rebellion and provides perfect grounds for his impeachment."

Impeaching him would require support from two-thirds of the parliament, or 200 of its 300 members. The Democratic Party and other small opposition parties together have 192 seats. But when the parliament rejected Yoon's martial law declaration in a 190-0 vote, 18 lawmakers from Yoon's ruling People Power Party cast ballots supporting the rejection, according to National Assembly officials.

The leader of the People Power Party, Han Dong-hun, who has long ties with Yoon dating to their days as prosecutors, criticized Yoon's martial law declaration as "unconstitutional."

Plea for Cabinet members

If Yoon is impeached, he'll be stripped of his constitutional powers until the Constitutional Court can rule on his fate. Prime Minister Han Duck-soo, the No. 2 position in the South Korean government, would take over his presidential responsibilities. As calls mounted for Yoon's Cabinet to resign, Han issued a public message pleading for patience and calling for Cabinet members to "fulfill your duties even after this moment."

At least six of the Constitutional Court's nine justices need to support the motion filed by lawmakers for Yoon to be removed from office. But the court currently has only six justices following the retirements of three justices, which is one below the minimum seven needed to handle a presidential impeachment case, requiring lawmakers to speed up the process of naming new justices.

Yoon's martial law declaration, the first of its kind in more than 40 years, harkened to South Korea's past military-backed governments when authorities occasionally proclaimed martial law and other decrees that allowed them to station combat soldiers, tanks and armored vehicles on streets or at public places like schools to prevent anti-government demonstrations. Such scenes of military intervention had not been seen since South Korea achieved a genuine democracy in the late 1980s until Tuesday night.

After Yoon's declaration, troops carrying full battle gear, including assault rifles, tried to keep protesters away from the National Assembly as military helicopters flew overhead and landed nearby. One soldier pointed his assault rifle at a woman who was among protesters outside the building demanding that the martial law be lifted.

It wasn't clear how the 190 lawmakers were able to enter a parliamentary hall to vote down Yoon's martial law decree. Opposition leader Lee Jae-myung livestreamed himself climbing over the wall, and while troops and police officers blocked some from entering they didn't aggressively restrain or use force against others.

No major violence has been reported. The troops and police personnel were later seen leaving the grounds of the National Assembly after the parliamentary vote to lift the martial law.

National Assembly Speaker Woo Won Shik said: "Even with our unfortunate memories of military coups, our citizens have surely observed the events of today and saw the maturity of our military."

WATCH | Korean community in B.C. concerned about political unrest: 

Koreans in B.C. share their concerns about South Korea's political unrest

Concerns are mounting within B.C.'s Korean community after South Korea's president imposed martial law overnight. The law has since been lifted following political backlash and large protests in the country. As Jon Hernandez reports, many hope the quick resolution is a sign the country's democratic government is holding.

Under South Korea's constitution, the president can declare martial law during "wartime, war-like situations or other comparable national emergency states" that require the use of military force to restrict the freedom of press, assembly and other rights to maintain order. Many observers question whether South Korea is currently in such a state.

The constitution also states that the president must oblige when the National Assembly demands the lifting of martial law with a majority vote.