North Korean leader Kim Jong Un on Sunday placed the city of Kaesong near the border with South Korea under total lockdown after a person was found with suspected COVID-19 symptoms.
If the person is officially declared a virus patient, he or she would be the North's first confirmed coronavirus case.
North Korea has said it has no single virus case on its territory, a claim questioned by outside experts.
"To tackle the present situation, he (Kim) declared a state of emergency in the relevant area and clarified the determination of the party central committee to shift from the state emergency anti-epidemic system to the maximum emergency system and issue a top-class alert," the KCNA reported.
"All the persons in Kaesong city who contacted that person and those who have been to the city in the last five days are being thoroughly investigated, given a medical examination and put under quarantine," the North's state media said.
"Despite the intense preventive anti-epidemic measures taken in all fields throughout the country and tight closure of all the channels for the last six months, there happened a critical situation in which the vicious virus could be said to have entered the country," Kim was quoted as saying.
Describing its anti-virus efforts as a "matter of national existence," North Korea earlier this year shut down nearly all cross-border traffic, banned foreign tourists and mobilized health workers to quarantine anyone with symptoms.
But the Kaesong lockdown is the first such known measure taken in a North Korean city to stem the pandemic.