Long queues of voters were seen at several polling stations in the capital Seoul, although unlike in the past, this year's early voting is being held entirely on weekdays, Yonhap News Agency reported.
Early voting began at 3,568 polling stations nationwide as voters prepare to elect a successor to former President Yoon Suk Yeol for a five-year term.
Yeoul was ousted over his abortive attempt to invoke martial law in December.
The two-day early voting period will end at 6 pm local time Friday (0900GMT), according to the National Election Commission (NEC).
Currently, six hopefuls are vying for the country's top office, but the actual contest is between two candidates.
The latest poll released Wednesday showed Democratic Party (DP) candidate Lee Jae-myung leading with 49.2%, followed by Kim Moon-soo of the ruling People Power Party with 36.8%.
Lee Jun-seok of the New Reform Party is third with 10.3%.
The DP's Lee will cast his ballot Thursday in Sinchon, western Seoul, while Kim is scheduled to vote in Incheon's Gyeyang district during his campaign stop there.
The presidential election is scheduled for June 3.
AzVision.az
More about: SouthKorea
