SEOUL — North Korea went into emergency mode Thursday with its first acknowledgement that there is at least one case of Covid-19 in the country.

Pyongyang’s Korean Central News Agency did not say who was diagnosed or where, but fear of a mass outbreak was evident. The country’s leaders, the dispatch said, discussed “coping with the situation of an epidemic prevention crisis facing the country.”

Kim Jong-un, who rules as general secretary of the Workers’ Party, among other titles, wore a face mask as he presided over the meeting that “recognized the most serious state emergency incident has occurred,” KCNA reported.

North Korea has been assumed to have been battling the spread of Covid ever since suddenly closing its borders with its patron state China as the virus was spreading rapidly from its source in the industrial city of Wuhan. While shutting down access even to diplomats and delegations from friendly countries, Mr. Kim’s regime steadfastly claimed to have prevented the virus from getting loose among his poverty-stricken people and even rejected donations of vaccines from South Korea and other sources.

The North as of Thursday was no longer in denial. KCNA, in a report disseminated in English, said “a hole was broken in our emergency epidemic prevention front which has firmly been defended for two years and three months from February 2020.”

The dispatch left no doubt that heads would roll in a blame game in which those below the top leadership would have to take full responsibility.

The politburo, KCNA said, “criticized the epidemic prevention sector for its carelessness, slackness, irresponsibility and incompetence as it failed to sensitively cope with the public health situation.” Health officials were all the more culpable, the dispatch indicated, considering “an increase in the number of those infected with all kinds of mutated viruses worldwide including the surrounding regions of our country.”

Fear about the spread of the virus was likely to put a crimp in possible plans for conducting the North’s seventh nuclear test, for which Mr. Kim is widely assumed to be preparing, but that did not stop him from ordering more missile tests.

South Korea’s military command reported that North Korea on Thursday fired a ballistic missile off its east coast but did not say what kind, according to the South’s Yonhap news agency. North Korea on Saturday test-fired a submarine-launched ballistic missile capable of being launched from a submarine close to the shores of target countries.

North Korea has conducted numerous missile tests this year, but the latest appeared to have been timed to coincide with the inauguration on Tuesday of the conservative Yoon Suk-yeol as South Korea’s president. He promised to adopt a hard-line policy toward the North but extended an olive branch, promising aid provided the North gives up its nuclear-and-missile program.

South Korea was expected to renew its offer to send vaccines to the North while demanding signs of concessions.

Kim Jong-un did not talk about vaccines, saying simply “the current epidemic crisis” and “maximum epidemic prevention system is mainly aimed at stably containing and controlling the spread of Covid-19,” according to KCNA.

Mr. Kim cautioned against “unscientific fear, lack of faith and weak will” — strong words that left no doubt of the incipient sense of panic in his country.

NK News, a website in Seoul that closely tracks North Korea, quoted sources reporting a “nationwide lockdown” as of two days ago. “Multiple sources in Pyongyang,” said NK News, “have reported panic buying and supply shortages surrounding uncertainty about when the lockdown might end.”