The measure was taken on Friday afternoon after a resident of Kaesong who is suspected of fleeing the country to South Korea years ago, illegally crossed the border into North Korea early last week, said North Korea’s Central News Agency (KCNA).
State media said the resident was found with suspected Covid-19 symptoms.
If the resident tests positive for the virus, it would make them North Korea’s first confirmed coronavirus case, though outside experts have questioned the country’s reporting on infections.
The news agency said respiratory secretion and blood tests showed the person “is suspected to have been infected” with the virus.
It said the suspected case and others who were in contact as well as those who have been to Kaesong in the last five days were placed under quarantine.
North Korean leader Kim Jong Un convened an emergency politburo meeting on Saturday in response to what he described as a “critical situation in which the vicious virus could be said to have entered the country”.
Mr Kim ordered a “maximum emergency system” to contain the spread of the virus and imposed a lockdown in the border town.
He also warned those who assisted with any illegal border crossings would receive “a severe punishment”.
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 mobilised health workers to quarantine anyone with symptoms.
Choo Jae-woo, a professor at Kyung Hee University, told Reuters: “It’s an ice-breaking moment for North Korea to admit a case.
“It could be reaching out to the world for help. Perhaps for humanitarian assistance.”
Earlier this month, Mr Kim urged officials to stay alert over the coronavirus threat, warning that complacency risks “unimaginable and irretrievable crisis”.
Additional reporting by Associated Press.