SEOUL — South Korea's main parties are holding emergency meetings amid reports MPs could bring forward a vote to impeach President Yoon Suk Yeol over Tuesday night's short-lived martial law declaration.

The main opposition Democratic Party says the vote, currently scheduled for Saturday, could take place as soon as it can guarantee the numbers to pass the motion.

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" if he remained in power.

The opposition needs the support of at least eight ruling party MPs to secure the 200 votes required for the impeachment motion to pass.

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

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

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."

He added that his party had learned about plans to jail arrested opposition politicians in a detention center in Gwacheon, a city south of Seoul.

His comments are the first clear indication the president's own party may now vote to help impeach him.

Earlier on Friday, supporters of the opposition assembled on the steps of parliament, armed with placards and demanding the president's removal.

Yoon's attempt to impose martial law shocked the country and unnerved South Korea's allies and financial markets.

He cited threats from "anti-state forces" and North Korea. But it soon became clear that his move had been spurred not by external threats but by his own domestic political troubles.

The order was abruptly reversed hours later after 190 MPs managed to make it into the parliament and vote it down - some of them climbing fences and breaking barricades to get into the chamber.

Opposition lawmakers are concerned that there will be another attempt to impose martial law. Some of them earlier told BBC they have been staying close to the National Assembly grounds so they could get there quickly to vote down any such declaration.

Special forces commander Kwak Jong-kuen on Friday assured parliament he would refused to follow such an order if martial law was declared again.

Kwak said he rejected orders to remove MPs from the assembly floor while they were gathering to vote down the martial law declaration early on Wednesday.

"I ordered soldiers not to enter the floor... I ordered that no live ammunition be given out [and] that no harm must come to the civilians," he said.

Meanwhile, ruling party MP Cho Kyung-tae became 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.

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.

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. — BBC