The first local cases of COVID-19 transmission within a school were reported on Tuesday.
Two elementary school students in the central city of Daejeon were infected as a confirmed fifth grader had reportedly been attending the school for three days in late June.
One is a classmate of the first student and authorities say they were regularly in close contact.
The other student is in a different class, but shared the same gym as the first student.
That first student is believed to have come into contact with more than 150 students.
All of them and the other fifth graders in the school are due to be tested.
The first student was confirmed to have COVID-19 on Monday.
Officials say he caught it off another family member.
The brother of the student, who is in the third grade of middle school, has been confirmed to have the virus as well.
The city will close 14 elementary and middle schools in the surrounding area and resume home schooling until August.
In the southwest of the country, the city of Gwangju has recorded a double-digit number of new cases for the first time.
The city, which had previously seen less than 50 cases in total before this spike, reported 12 new cases on Wednesday.
Authorities have pointed toward a local temple and door-to-door sales company for the reason behind the spike.
The country as a whole reported 51 new cases on Wednesday.
The total stands at 12,850 with the death toll remaining at 282.
Kim Do-yeon, Arirang News.