South Korean President Park Geun-hye is scheduled to face an impeachment vote on Friday over a scandal that could lead to her becoming the country's first democratically elected leader to be removed from office in disgrace.

The parliamentary vote is scheduled to begin at 06:00 GMT, and if the motion passes with a two-thirds majority, the country's Constitutional Court will have up to 180 days to determine whether to formally end Park's presidency.

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Prosecutors say Park colluded in the criminal activities of a longtime confidante to manipulate government affairs and extort businesses.

The confidante, Choi Soon-sil, the daughter of a cult leader who mentored Park before his death, has been indicted on a string of charges including abuse of authority and attempted fraud.

The president is also suspected of having put pressure on top Korean companies, including the electronics giant Samsung, to donate to two foundations controlled by Choi and allegedly set up to back Park's policy initiatives. 

Park, who has immunity from prosecution while in office, has repeatedly apologised but has refused to meet prosecutors investigating the scandal.

Al Jazeera's Harry Fawcett, reporting from the National Assembly in Seoul, said some members of Park's conservative Saenuri Party would have to break rank for the vote to pass.

"What is required is 28 members of the ruling Saenuri Party vote along with 172 opposition and independent members of the national assembly in order to get the two-thirds majority required," he said.

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The leaders of the two main opposition parties have said their 159 members would all resign if the impeachment motion failed, taking responsibility for their inability to follow through on the demands of the public.

Parliament introduced the impeachment bill on Thursday and it must be voted on within 24 to 72 hours.

If the motion passes, the Constitutional Court will determine whether parliament followed due process and whether there are sufficient grounds for impeachment, a process that will involve arguments from the two sides in public hearings.

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Prime Minister Hwang Kyo-ahn, who holds what is largely a ceremonial role, would assume interim presidential powers while the court deliberates.

There have been mass rallies every Saturday for the past six weeks calling for Park to quit, and opinion polls show overwhelming public support for her impeachment.

A poll released on Friday showed her approval rating stood at 5 percent, a slight improvement from a record low of 4 percent.

South Korea's economic outlook is worsening too, partly owing to the internal political uncertainty, as well as worries over the potential effect of US President-elect Donald Trump's policies on trade and foreign affairs.

The nine-member court is considered conservative in its makeup but some of its former judges have said the case against Park is strong and is likely to be approved.

The Bank of Korea will hold emergency meetings to review policy measures that may be taken against any fallout from the vote, a central bank official said.

Source: Al Jazeera News