INCHEON -- More than 20 students of an elementary school here have been infected with the new coronavirus, authorities said Tuesday, ordering emergency COVID-19 tests for all its students and teachers and their families.

According to the municipality of Incheon, 40 kilometers west of Seoul, 23 sixth graders of Inju Elementary School in the city's central ward of Michuhol have been diagnosed with COVID-19 this week.

The municipality plans to install a walk-through screening station at the school Tuesday morning to facilitate the testing of all of its students and teachers and their families, estimated to total about 3,000.

The apparent cluster of infections began Monday when two sixth graders tested positive for COVID-19 after displaying suspected coronavirus symptoms, such as fever and muscle pain, days earlier.

Municipal authorities then conducted coronavirus tests on 55 other sixth graders suspected of being exposed to the two infected students, and 21 of them were confirmed to be infected on Tuesday.

Five other students had "undecided" test results and are still waiting for the final results, they said, adding an investigation is under way to see if the mass infections of students were related to the more contagious delta coronavirus variant.

South Korea's daily new virus cases have stayed above 700 for the past week due to a sharp spike in new cases in the greater Seoul area that includes Incheon. (Yonhap)