South Korea reported 437 new infections on Monday, up 45 from the previous day.
A cluster infection at an unauthorized missionary training school over the weekend in the city of Daejeon has led to at least 127 cases so far.
The outbreak was first reported on Saturday at the school's boarding facility run by a society called 'IM' that recruits teenagers aged 16 to 18 to be trained as international Christian missionaries.
116 students, which is about 97 percent of those enrolled, and 11 staff members have tested positive.
One student had suspected symptoms on January 12th and around five others began showing symptoms by the weekend but the school did not instruct them to get tested or go for treatment.
Prime Minister Chung Sye-kyun called for fast and stern action as the school is part of a nationwide network.
"The most important thing is a prompt response to curb the spread. We have to make sure it doesn't become another Shincheonji religious outbreak like we had last year."
The school has reportedly been in violation of COVID-19 measures where 159 students and teaching staff live.
According to authorities, the rapid spread of the virus was mainly due to small living spaces compared to the number of students.
The Daejeon city government said that around 120 students have been living in dormitories and between seven and 20 students in single-dorm rooms since January 4th.
Many of them reportedly have had to share bathrooms and no partitions have been installed at the dining tables in the cafeteria.
The health authorities will carry out inspections at similar educational facilities nationwide and come up with quarantine measures.
Eum Ji-young, Arirang News.