Health officials in South Korea believe the country is going through a second wave of coronavirus, despite recording relatively low numbers.
The country had been a success story in dealing with Covid-19, but now expects the pandemic to continue for months.
Head of the Korea Centers for Disease Control (KCDC), Jung Eun-kyeong, said the first wave lasted up until April.
Yet since May, clusters of new cases have grown, including outbreaks at nightclubs in the capital, Seoul.
Between those periods, daily confirmed cases had fallen from nearly a thousand to zero infections recorded for three days in a row.
Officials on Monday said that over the last 24 hours, 17 new infections had been recorded, from different clusters in large offices and warehouses.
Dr Jeong said the recent resurgence had led her to conclude that the country was in the grip of a second wave of the virus, and that she expected it to continue.
Until now, the KCDC had said that South Korea's first wave had never really ended.
But Dr Jeong said it was now clear that a holiday weekend in early May marked the beginning of a new wave of infections focused in the greater Seoul area, which had previously seen only a few cases.