A recent rise in coronavirus cases among high school students raised alarm about a bigger risk to school safety, as more schools are considering larger in-person instruction in the upcoming fall semester.

According to health officials and municipal governments on Thursday, five high school students in Yongin, south of Seoul, have tested positive this week.

The first patient was confirmed to have the virus on Monday, and four more -- one classmate and three from a different school -- were confirmed the next day. All five are friends.

In a separate case, a high school student who lives in Goyang, northwest of Seoul, tested positive last Wednesday after the student's mother was confirmed to have been infected with the coronavirus earlier in the day. On Thursday, the student's schoolmate also tested positive.

In both cases, the teenagers were having in-person classes.

While health officials were studying how they became infected with the virus, the Ministry of Education cautiously predicted that they could have been infected while hanging out after school.

"In the Goyang case, the two are close friends who go to cram schools and hang out together after school," an official from the ministry said. "The five students in Yongin began showing symptoms after they spent time together during weekends, so we cannot rule out transmissions outside school."

The two cases have unsettled educators, health authorities and parents alike, as most schools are scheduled to end summer vacations and open for the fall semester at the end of this month.

In the provinces with dwindling coronavirus caseloads, which exclude the capital Seoul and its adjacent cities, some education offices strongly recommend that schools in their districts switch back to in-person instruction, largely due to a widening gap in learning.

The ministry said the decision lies with each autonomous office as to what type of instruction it will institute in the upcoming session. But it strongly recommended a cap on student numbers at two-thirds of full attendance for large-scale schools with more than 1,000 students and classrooms with more than 30 students.

Experts warned that schools should remain cautious about full-scale reopening in the middle of the pandemic.

"COVID-19 infections are likely to increase in cooler weather," Kim Woo-joo, a professor for infectious diseases at Korea University in Seoul, said. "Just because there weren't big school infections in the first semester, that does not mean it is safe to go for full reopening in the coming one." (Yonhap)