The country reported 2,383 new COVID-19 cases, including 2,356 local infections, bringing the total caseload to 303,553, according to the Korea Disease Control and Prevention Agency (KDCA).
The daily caseload touched a fresh high of 3,272 on Saturday before slightly falling to 2,771 on Sunday.
But health authorities predicted new cases may sharply rise from the middle of this week due to delta variants and the aftermath of a mass migration during the Chuseok holiday, the Korean autumn harvest celebration, which ran from Monday to Wednesday last week.
Daily cases have stayed over 1,000 for the last 83 days although the country implemented tough virus curbs to slow down the nationwide spread.
The country added six more deaths from COVID-19, raising the death toll to 2,456.
The greater Seoul area, the hotbed of South Korea's latest wave of the pandemic, has been under Level 4 distancing measures, the highest in the country's four-tier system, since July, with most other areas being under Level 3.
Private gatherings are allowed with a maximum of six people on the condition that four of them are fully vaccinated.
The Seoul metropolitan area, home to half of the nation's 52 million population, accounted for 71 percent of the total infections.
Seoul reported 773 cases, and the surrounding Gyeonggi Province 755 cases, with the western port city of Incheon adding 145 cases.
A total of 38.09 million people, or 74.2 percent of the country's population, have received their first shots of COVID-19 vaccines, and 23.23 million people, or 45.3 percent, have been fully vaccinated, the KDCA said.
In a bid to achieve herd immunity by the end of October, the health authorities will announce a plan to vaccinate pregnant women and people aged between 12 and 17, as well as to administer booster shots to people aged over 60 and older and medical workers in the October-December period.
Imported cases came to 27, including eight from the Philippines.
The number of patients with serious symptoms across the country reached 319, down one from the previous day.
The total number of people released from quarantine after making full recoveries was 269,132, up 992 from a day earlier. (Yonhap)