Students sit behind protective shields as a preventative measure against the COVID-19 novel coronavirus in a classroom in Daejeon, South Korea on May 20, 2020. (STR / YONHAP / AFP)

SEOUL - South Korean high schools opened on Wednesday for the first time this year, with mask-wearing seniors returning to class in the vanguard of a phased plan to reopen all schools under strict protocols to prevent the spread of the novel coronavirus.

The beginning of the spring semester has been postponed several times since March as South Korea battled the coronavirus outbreak, with classes held online.

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From now on, we are entering an important phase where we need to succeed in both studies and (coronavirus) prevention

Cho Hee-yeon, Superintendent of Seoul Metropolitan Office of Education

But with daily coronavirus cases sharply down since a February peak, teachers with thermometers and hand sanitisers welcomed seniors in masks at their high schools on Wednesday.

“Schools have been anxiously waiting for all you students for the past three months,” Cho Hee-yeon, superintendent of Seoul Metropolitan Office of Education, told students at a high school entrance.

“From now on, we are entering an important phase where we need to succeed in both studies and (coronavirus) prevention.”

Some students put their arms around their friends’ shoulders but teachers told them to keep their distance. Private sanitation contractors on motorcycles drove back and forth spraying disinfectant.

Under new health guidelines for schools, students and teachers must wear masks except at mealtimes, and are asked to wipe down their desks. Windows will be open to improve air-flow, and desks spaced 1 meter (3 feet) apart.

Starting with high school seniors, schools will reopen in stages between May 20 and June 1 for all 5.5 million elementary, middle and high school students.

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A staff member (center right) greets students as they arrive at Kyungbock High School in Seoul on May 20, 2020. (ED JONES / AFP)

The education ministry keeps track of whether teachers or students have a fever using an online self-diagnostic system and anyone with a temperature over 37.5 degrees Celsius (99.5 degrees Fahrenheit) must stay home.

If any student tests positive for the virus, the entire school will switch to online classes until it is deemed safe for students to return.

Korea reported 32 new cases as of midnight Tuesday, taking the national tally to 11,110, with 263 deaths.

Students sit behind protective screens as a preventative measure against the COVID-19 novel coronavirus as they eat lunch at a high school in Daejeon, South Korea on May 20, 2020. (YONHAP / AFP)

Senior students maintain a social distance as they arrival at Hamwol High School in Ulsan, South Korea, May 20, 2020. (KIM YONG-TAE/YONHAP VIA AP)

Students observe social distancing as a preventative measure against the COVID-19 novel coronavirus as they eat lunch at a high school in Seoul on May 20, 2020. (YONHAP / AFP)

Students wearing facemasks amid concerns over the COVID-19 novel coronavirus undergo a temperature check as they arrive at Keongbok High School in Seoul on May 20, 2020. (ED JONES / AFP)