Schools will return to a mix of online and offline classes from Monday, as the country reinstates stricter social distancing measures due to rising cases of COVID-19.

The Ministry of Education announced Thursday that schools in Korea will reduce student density to prevent classroom transmissions starting Monday, less than a month after schools returned to in-person classes on Nov. 22.

The ministry said as the rate of transmission in schools is not high, they will continue to have in-person classes, but in smaller sizes.

Elementary schools will maintain a five-sixths level of class density, as first and second graders are to have full-fledged classes while older grades, only two in three students will be allowed to attend in-person classes. Those at home will keep up with the curriculum through online classes.

For middle and high schools, maintaining a two-thirds class density level is suggested.

“Schools can have about three days of preparation period before implementing the new measure,” an official from the Education Ministry said during a press briefing held Thursday.

Kindergartens, special schools for disabled and more will continue to have full-fledged, in-person classes.

Students who attend schools where they are set to be vaccinated through the ministry-led outreach vaccination program will be excluded from the density level calculation.

The Education Ministry said that while provincial education offices and individual schools will be allowed to adjust the class density level flexibly depending on the situation, it advises against having online-only classes.

The new measures will end when schools go into winter vacation.

Some 20 percent of schools will go into winter vacation in the fourth week of December, while more than 40 percent will end the term in the following week. The rest of the schools will begin vacation in January.

The ministry suggests schools separate students by groups during end-of-term exams. It said that 16.2 percent of middle schools and 17.2 percent of high schools will have end-of-term exams after Monday based on a report from April.

The ministry also advised colleges to have some classes go online during the winter vacation period. In-person classes will have students leave an empty seat between each other.

Over the past week, 6,084 kindergarten, elementary, middle and high school students were confirmed to have COVID-19. The average daily case number among students was 869.1, more than double the number before schools returned to in-person classes in late-November.