Polls opened early Wednesday as South Koreans began voting for their next president, with a close battle between the two leading candidates, liberal Lee Jae-myung and conservative Yoon Suk-yeol.
An additional 90 minutes will be allocated after closing when Covid positive voters will be able to cast their ballots.
The record early voting indicates turnout will be high after a campaign dominated by insults between Lee of the ruling Democratic Party and Yoon of the opposition People Power Party.
The first voters arrived at the polling stations while it was still dark, lining up at the polling stations wearing their masks.
South Korea is in the grip of a wave of Omicron Covid, with more than 200,000 new virus cases recorded most days this month.
More than a million people are currently isolated at home after testing positive, health authorities say. The country changed its electoral laws last month to ensure they could vote.
In a two-day early voting exercise last week, a record 37 percent of the 44 million eligible people cast ballots, the highest number since the system was introduced in 2013.
Surveys show that the top concerns among the electorate are skyrocketing house prices in the capital Seoul, rising domestic inequality and stubborn youth unemployment.