South Korean public in ‘great danger’ if president stays, says party boss

South Korea's President Yoon Suk Yeol ordered the arrest of his own ruling party's leader Han Dong-hoon when he declared martial law on Tuesday night.

The arrest list also included the leader of the main opposition Democratic Party, Lee Jae-myung, as well as three opposition lawmakers, the National Intelligence Service deputy director said.

The president tried to "use this chance to arrest them and wipe them out", said director Hong Jang-won.

The revelation came as the country's political parties held emergency meetings throughout Friday, with MPs planning to bring a vote to impeach Yoon. The motion, which is scheduled for Saturday, will pass if two-thirds of MPs vote for it.

The opposition have a majority in the 300-seat parliament but need the support of at least eight ruling party MPs to secure the 200 votes required for the impeachment motion to pass.

In the first clear sign his own party may now vote with the opposition, the leader of Yoon's ruling party called for his swift suspension on Friday, saying he posed a "great danger" to democracy if he remained in power.

Han Dong-hoon, chief of the People Power Party (PPP), had earlier in the week said his party would not support the opposition's impeachment motion.

But on Friday he announced there was "credible evidence" that Yoon had ordered the arrest of key politicians - including himself- on "anti-state charges" on Tuesday.

Han said Yoon had planned to jail arrested politicians in a detention centre in Gwacheon, a city south of Seoul.

He expressed concern that "extreme actions", such as the martial law declaration, could be repeated if Yoon remained in office.

"[These are] putting the Republic of Korea and its people at great risk.

The capital, Seoul, has seen more than two days of street protests demanding Yoon's resignation, while police said he is being investigated for "insurrection".

People have also been flooding PPP lawmakers with text messages, urging them to vote for Yoon's impeachment, according to South Korean media reports.

One MP, Shin Sung-bum, received more than 4,000 such messages on Facebook, The Chosun Daily reported.

Cho Kyung-tae was the first ruling party MP to publicly voice support for Yoon's impeachment.

"The choice between standing on the side of the people by suspending the president's duties or becoming an ally of the forces that imposed martial law is a matter for politicians to judge," Cho said on Friday.

"I hope that all the politicians of the People's Power will stand on the side of the people," he added.

More than seven out of 10 South Koreans were in favour of the impeachment, a survey by local pollster Realmeter showed on Thursday.

Yoon has not been seen or spoken publicly since reversing the martial law order early on Wednesday. A survey conducted from Tuesday to Thursday this week showed his approval rating had tumbled to a record low of 13%.

Before his attempt to place the country under military rule, the president had already been beset by low popularity ratings, corruption allegations and an opposition-led legislature that reduced him to a lame-duck leader.

Additional reporting by Hosu Lee in Seoul and Fan Wang in Singapore