At least six people have now died and hundreds of thousands of people are showing fever symptoms after North Korea declared a "grave state emergency" with the confirmation of its first Covid case.
North Korea state media said there had been an "explosive spread" of fever as fears rise over the scale of outbreak.
Some 187,800 people are currently being treated in isolation after a fever of unidentified origin has "explosively spread nationwide" since late April, the official KCNA news agency reported.
Around 350,000 people have shown signs of that fever, including 18,000 who newly reported such symptoms on Tuesday alone, KCNA said.
About 162,200 of them have been treated so far, but it did not specify how many had tested positive for Covid.
At least six people who showed fever symptoms died, with one of those cases confirmed to have contracted the Omicron variant of the virus, KCNA said.
North Korean leader Kim Jong Un visited the anti-virus command centre to check the situation and responses after declaring "gravest state emergency" and ordering a national lockdown.
North Korea has said the outbreak began in the capital of Pyongyang in April.
State media did not elaborate on the cause of the outbreak, but the city hosted several massive public events on April 15 and 25, including a military parade and large gatherings where most people did not wear masks.
Kim "criticised that the simultaneous spread of fever with the capital area as a centre shows that there is a vulnerable point in the epidemic prevention system we have already established," KCNA said.
Kim singled out actively isolating and treating people having fever as a top priority, while calling for devising scientific treatment methods and tactics "at a lightning tempo" and bolstering measures to supply medications.
In another dispatch, KCNA said health authorities were trying to organise testing and treatment systems and bolster disinfection work.
The rapid spread of the virus highlights the potential for a major crisis in a country that lacks medical resources but had refused international help with vaccinations and kept its borders shut.
Analysts said the outbreak could threaten to deepen the isolated country's already tough food situation this year, as the lockdown would hamper its "all-out fight" against drought and the mobilisation of labour.
North Korea had declined vaccine supplies from the COVAX global sharing programme and China, possibly leaving the vast majority of people in a relatively young society at higher risk of infection.
Kwon Young-se, South Korea's new nominee to be the unification minister, responsible for inter-Korean ties, said at his confirmation hearing on Thursday that he was willing to push for humanitarian assistance for the North, including COVID treatment, syringes and other medical supplies.
A US State Department spokesperson said it had no plans to send vaccines to North Korea but supported international efforts to provide aid to vulnerable people there, urging Pyongyang to facilitate that work.
