South Korean ruling party to oppose Yoon's impeachment

South Korea's parliament has formally introduced a motion to impeach President Yoon Suk-yeol over a botched attempt to impose martial law but his party has vowed to oppose the move, throwing the process into doubt.

MPs could vote for the bill as early as Friday but Yoon's ruling People Power Party said they would oppose it.

The opposition Democratic Party, which has a majority in parliament, needs at least eight ruling party MPs to back the bill in order for it to pass.

"The Yoon Suk-yeol regime's declaration of emergency martial law caused great confusion and fear among our people," Democratic Party MP Kim Seung-won told a late night session of South Korea's National Assembly, held in the early hours of Thursday morning.

None of the 108 ruling party MPs were present for the introduction of the motion.

"We need to immediately suspend the authority of President Yoon. He has committed an indelible, historic crime against the people, whose anxiety needs to be soothed so that they can return to their daily lives," Kim said.

If the impeachment motion is passed and upheld by the constitutional court, Yoon would be the second South Korean president to have been impeached since massive candlelit protests against an influence-peddling scandal led to the removal of former president Park Geun-hye in 2017.

Yoon's declaration of martial law late on Tuesday attempted to ban political activity and censor the media in South Korea, which has Asia's fourth largest economy and is a key US ally.

The shock move divided Yoon's ministers and his ruling People Power Party and unleashed six hours of political chaos.

Armed troops forced their way into the National Assembly building in Seoul but stood back when parliamentary aides sprayed them with fire extinguishers.

MPs rejected the martial law decision while protesters scuffled with police outside.

Demonstrators held candlelit vigils in Seoul late on Wednesday and called for Yoon's resignation.

The impeachment motion against Yoon was reported to a plenary session that opened shortly after midnight on Thursday and paved the way for an impeachment vote to be held in the following 24 to 72 hours.

Opposition parties need a two-thirds majority to pass the bill, and support from about eight members from Yoon's own party to secure the necessary 200 votes to impeach him.

If the bill passes, South Korea's Constitutional Court will then decide whether to uphold the motion - a process that could take up to 180 days.

If Yoon were to be suspended from exercising power due to parliament passing the bill, Prime Minister Han Duck-soo would fill in as leader.

If the embattled president resigned or was removed from office, a new election would be held within 60 days.