SEOUL — North Korea on Thursday reported its first outbreak of the coronavirus, declaring a “maximum emergency” and ordering all cities and counties in the nation of 25 million to lock down to fight the spread.

It was an abrupt change for a secretive country that had long insisted it had no cases of the virus that first emerged in neighboring China more than two years ago. Outside experts had been skeptical, however, citing a lack of extensive Covid testing and the North’s threadbare public health system.