South Korea’s President Yoon Suk Yeol is facing mounting pressure from the nation’s main opposition, the Democratic Party of Korea, with demands for impeachment or even charges of treason after his brief attempt to impose martial law, which was blocked by the National Assembly overnight December 3-4.

The move stunned the nation. Many were already in bed and only realised what was going on the following morning, Wednesday December 4, as it marked the first time martial law had been declared since South Korea’s current democratic system was introduced in 1987.

Around 300 Korean troops soon entered the National Assembly compound, sparking widespread shock and condemnation.

The declaration, however, was short-lived and by the early hours of December 4, the National Assembly rejected the move in a 190-0 vote. A number of the president’s ruling People Power Party (PPP) joined the opposition in the one-sided vote.

The martial law decree was later lifted by the president and in the almost 12 hours since protests have taken place around the central government building in Seoul.

As daylight broke, however, opposition lawmakers were openly calling for his removal from office with the DPK announcing plans to file treason charges against Yoon, according to local media agency Yonhap.

Yoon’s defence and interior ministers were also included in these statements after DPK leader Lee Jae-myung labelled the martial law declaration “illegal”, before adding that Yoon is "no longer the president" of South Korea, reported the Korea Times.

For an impeachment motion to carry in South Korea, lawmakers must vote within 72 hours of it being reported to the plenary session. This must be followed up with a two-thirds majority of the 300-member assembly voting in favour.

However, with the DPK and other opposition parties together holding 192 seats, eight or more of the PPP’s own lawmakers would need to break ranks for it to carry.

A Constitutional Court would then determine if and how President Yoon should be removed from office.