The daily increase of COVID-19 cases in South Korea climbed back to the mid-100s amid continued sporadic group infections in the Seoul metropolitan area.

The Korea Disease Control and Prevention Agency(KDCA) said as of 12:00 a.m. Thursday, 153 additional people tested positive, raising the country's accumulated total cases to 22-thousand-657.

The daily increase has been gradually declining to the low-100s since 176 reported last Friday.

Out of 145 local infections, 121 were from the Seoul metro area. Capital region infections climbed back to triple digits after staying in double digits for the past five consecutive days.

At least ten new cases were reported in connection to a Kia Motors plant in Gwangmyeong, Gyeonggi Province, and 20 have so far been confirmed linked to a nursing facility in the Gyeonggi provincial city of Icheon.

Authorities are particularly concerned about the fact that the route of infection remains unknown for over 25 percent of the cases.