North Korea officially confirmed its first COVID-19 outbreak on Thursday and ordered a national lockdown, with state media reporting a sub-variant of the highly transmissible Omicron virus had been detected in the city of Pyongyang.

"There has been the biggest emergency incident in the country, with a hole in our emergency quarantine front, that has been kept safely over the past two years and three months since February 2020," official KCNA news agency said.

The report said people in Pyongyang had contracted the Omicron variant, without providing details on case numbers or possible sources of infection. The samples of the infected people were collected on May 8, it said.

The report was published as the North Korean leader Kim Jong Un chaired a Workers' Party meeting to discuss responses to the first outbreak of the coronavirus.

Kim ordered all cities and counties of the country to "strictly lock down" their regions to prevent the spread of the coronavirus and said emergency reserve medical supplies would be mobilised, according to KCNA.

Although the North has never confirmed a single coronavirus infection in the country, officials in South Korea and the United States have cast doubts, especially as cases of the Omicron variant were widely reported in neighbouring South Korea and China.

North Korea has declined shipments of vaccine from the COVAX global COVID-19 vaccine-sharing programme and the Sinovac Biotech vaccine from China. 

Kim told the Workers' Party meeting the latest emergency quarantine system's purpose is to stably control and manage the spread of the coronavirus and quickly heal infected people to eliminate the source of transmission in the shortest period, KCNA said.

A South Korea-based website that monitors activities in Pyongyang said this week that residents have been told to return home and remain indoors because of a "national problem" without offering details.

Earlier on Thursday, Chinese state television reported North Korea has required its people to stay at home since May 11 as many of them have "suspected flu symptoms", without referring to COVID-19.