South Korea on Wednesday reported 444 new cases of COVID-19, many of them among foreign workers at factories in the city of Dongducheon, north of Seoul.
That cluster emerged on Tuesday and has now grown to 105.
In response, the government is launching full inspections at more than a thousand businesses that are employing five or more foreign workers.
Also, with the weather warming up, social outings have increased, especially at the weekends, so the government is warning against complacency.