We're now getting pictures from our colleagues in Seoul showing protesters standing near the exits of the National Assembly to prevent members from leaving the building.
A little earlier, we reported all but one MP from the ruling People Power Party (PPP) had left the chamber. Two colleagues have since returned.
South Korean national assembly members in session as they vote for the impeachment of president yoon suk yeol
While President Yoon's declaration of martial late on Tuesday was seen as unacceptable by lawmakers of all stripes, the vote for him to be impeached has not been straightforward, says Sydney Seiler, Korea chair at the Center for Strategic and International Studies.
"It is a complex issue [which] touches on the standoff between the ruling and opposition parties," Seiler tells BBC News, noting the ruling party's official stance to vote against it.
He describes the martial law declaration as "using sledgehammer to push a pin in the wall".
"There was universal agreement that it was unacceptable, but political problems [between the parties have existed] before the martial law, and will continue," he says.
Still, Seiler adds he is optimistic that the "democratic mechanism that is in place [in South Korea] always works its way out".Kim Sang-wook, one of the ruling party MPs who re-entered the voting chamber, told reporters he had voted against the impeachment bill, in line with his party's official stance.
Journalists and party members gathered in the general assembly have opened up a channel to the chamber in the hopes that more members from the ruling People Power Party (PPP) will return.
The impeachment vote is being kept open in the hopes that more PPP members will come back and vote for it. They technically have until 00:48 (15:48GMT) to vote on the bill - which will be exactly 72 hours after the motion was put in.
Two PPP members have returned, making a total of three currently in parliament. The opposition needs eight PPP members to vote for President Yoon's impeachment in order for it to pass.
Journalists and party members gathered in the general assembly have opened up a channel to the chamber in the hopes that more PPP members will retur
Cho Kyung-tae was one of the first members of the ruling People Power Party (PPP) to say he would support the impeachment motion against President Yoon Suk Yeol.
Today, however, he joined other MPs from his party in leaving the chamber ahead of the impeachment vote.So why did he change his mind?
"I was determined to agree to the impeachment bill until yesterday, because there was no word from the president's office nor public apology for martial law or any follow-up measures," Yoon told BBC Korean ahead of the vote. "However, I heard that he was announcing an apology to the public today."
Yoon added that PPP party leader Han Dong-hoon's decision to not support the motion also contributed to his decision.
"Most members of the National Assembly acknowledge that the president's declaration of martial law was an incorrect and wrong action," he said. "However, there is concern that if impeachment is used as a means to address the president's wrongdoings, it will lead to an early presidential election."
Yoon noted that an early election could lead to the opposition party taking power, "creating a sense of unease".
"As a result, many members of the National Assembly find themselves in a very difficult situation and are reluctant to support impeachment," he explained.
If parliament does not vote for Yoon to be impeached today, the opposition will try again to call for a vote, opposition MP Joon Hyung Kim just told the BBC outside the voting chamber.
"Every week, we will do it until we succeed," said Joon, a member of the Rebuilding Korea Party.
Joon also called for members of the ruling party to "listen to the people", adding that he expects voting to go on until as late as midnight.
We earlier reported that four ruling People Power Party lawmakers had returned to the chamber to vote, based on local media reports.Local media have since retracted their reports about the fourth member.Only three PPP members are confirmed to have returned.
As one of the People Power Party members Kim Sang-wook re-enters the chamber, the protest rally's mood lifts instantly.
Hope ripples through the crowd. It goes wild as people begin cheering and chanting Kim's name like he's a rock star. Organisers begin playing K-pop songs and people start dancing, singing and waving their multicoloured light sticks. Some even start doing the Mexican wave to a Girls Generation song.
Suddenly a protest has become a pop concert on the streets.
Two more MPs from the ruling People Power Party (PPP) have just returned to the chamber, amid applause from opposition lawmakers.
That makes four PPP members who are currently seated in the National Assembly. The opposition needs eight PPP members to vote for President Yoon's impeachment in order for it to pass.
"Arrest Yoon Suk Yeol, impeach Yoon Suk Yeol!" they shout, calling for demonstrators to "surround the National Assembly".While the opposition MPs continue to cast their vote for the impeachment motion, Speaker Woo Won-shik of the Democratic Party has made a speech asking the ruling People Power Party members who walked out earlier to return to vote.
"The Republic of Korea is a democracy that's made of people's blood and tears," he said. "Are you not afraid of being judged by history, by the people, and by the world?"
"Participate in the voting, that's how you protect our democracy," he said.
Faced with the prospect that the impeachment vote may not take place, protesters are deeply disappointed. As the temperature drops even further, some are leaving the rally site, though many more have stayed on.
Freelance writer Park Ga-ram left her home in Daegu, a city about four hours drive from Seoul, at 5am today so she could take part in the rallies.
"I think the lawmakers are irresponsible," she said. "I am very disappointed because I was hoping for a good result. I'm left wondering how could this happen now." "I was waiting all day for this. I hope they go back and vote. I'm trying to stay hopeful, but I don't expect it to happen."
We’re outside the voting chamber in the parliament, where the ruling party members have been walking out one by one, boycotting the vote.
Lots of opposition party members are gathered here. They rushed up as soon as the MPs started leaving, trying to block their exits.They were chanting “traitors” and “get back in to vote”.
There is enormous anger. It seems there are only one or two ruling party members still left in the chamber, meaning this vote is now bound to fail.
A reminder that they do not have the required quorum to pass the bill, as all but one of the ruling party MPs left parliament ahead of the vote.
Outside the assembly, at the massive protest rally, a speaker is reading out the names of every People Power Party lawmaker.
"Go back in, join the vote," the crowds chant after the speaker reads out each name.
Of the 108 MPs from the ruling People Power Party (PPP), 107 have left the chamber. The party likely used a boycott strategy to prevent defections, as the impeachment vote is through anonymous ballots.
Ahn Cheol-soo, a professor-turned-politician who ran for the presidency in 2012, 2017 and 2022, is the only PPP member who remains in his seat.
Ahn has repeatedly said he would vote for impeachment if the president doesn't voluntarily step down before the voting.If the impeachment vote fails today - which is likely, given less than two thirds of parliament remain in the chamber - the next time the vote can take place is next Wednesday, 11 Dec.
Outside parliament, the crowd is continuing to grow as more Koreans converge on the avenue before the National Assembly. Police are stepping up controls.
The protest rally is right by a subway station, and major bottlenecks could be seen at the station exits earlier as people poured out.
Authorities have since closed the station, and police have formed lines along choke points to guide the crowd.
On the fenced-off main thoroughfare, where most of the crowd is sitting in neat rows, walking paths have been marked out with police tape. Text alerts about the crowd situation regularly pop up on our phones.
Seoul saw a deadly crowd crush two years ago at the Halloween celebrations in the Itaewon district. Everyone is trying to make sure that doesn't happen here.
