Six people have died and 350,000 have been treated for a fever that has spread "explosively" across North Korea, state media said Friday, a day after the country acknowledged a COVID-19 outbreak for the first time in the pandemic.

North Korea likely doesn't have sufficient COVID-19 tests and said it didn't know the cause of the mass fevers. But a big coronavirus outbreak could be devastating in a country with a broken health care system and an unvaccinated, malnourished population.

China's leaders are struggling to reverse an economic slump without giving up anti-virus tactics that shut down Shanghai and other cities, adding to challenges for President Xi Jinping as he tries to extend his time in power.

The ruling Communist Party has declared its "zero-COVID" goal of preventing all infections takes priority over the economy. It is a decision with global implications and comes despite warnings by experts including the head of the World Health Organization that the goal might be unattainable.

North Korea imposed a nationwide lockdown Thursday to control its first acknowledged COVID-19 outbreak after holding for more than two years to a widely doubted claim of a perfect record keeping out the virus that has spread to nearly every place in the world.

The outbreak forced leader Kim Jong Un to wear a mask in public, likely for the first time since the start of the pandemic, but the scale of transmissions inside North Korea wasn't immediately known. A failure to slow infections could have serious consequences because the country has a poor health care system and its 26 million people are believed to be mostly unvaccinated. Some experts say North Korea, by its rare admission of an outbreak, may be seeking outside aid.

China on Wednesday defended sticking to its strict "zero-COVID" approach, calling critical remarks from the head of the World Health Organization "irresponsible."

The response from the Foreign Ministry came after WHO Director-General Tedros Adhanom Ghebreyesus said he had been discussing with Chinese experts the need for a different approach in light of new knowledge about the virus.

Teams in white protective suits are entering the homes of coronavirus-infected people to spray disinfectant as Shanghai tries to root out an omicron outbreak under China's strict "zero-COVID" strategy.

City official Jin Chen said Tuesday that in older communities with shared bathrooms and kitchens, the homes of anyone else who uses those facilities will also be disinfected. He tried to address public concern about damage to clothing and valuables, saying residents can inform the teams about anything that needs protection.

China's export growth tumbled in April as global demand weakened, adding to pressure on the world's second-largest economy after Shanghai and other industrial cities were shut down to fight virus outbreaks.

Exports rose 3.7% over a year earlier to $273.6 billion, down sharply from March's 15.7% growth, customs data showed Monday. Reflecting weak Chinese demand, imports crept up 0.7% to $222.5 billion, in line with the previous month's growth below 1%.

South Africa on Thursday ended mask-wearing for school children despite a surge of infections driven by two new Omicron sub-variants of coronavirus. 

Climate change will result in thousands of new viruses spread among animal species by 2070 — and that's likely to increase the risk of emerging infectious diseases jumping from animals to humans, according to a new study.

This is especially true for Africa and Asia, continents that have been hotspots for deadly disease spread from humans to animals or vice versa over the last several decades, including the flu, HIV, Ebola and coronavirus.

Workers put up fencing and police restricted who could leave a locked-down area in Beijing on Tuesday as authorities in the Chinese capital stepped up efforts to prevent a major COVID-19 outbreak like the one that has all but shut down the city of Shanghai.

People lined up for throat swabs across much of Beijing as mass testing was expanded to 11 of the city's 16 districts.

Fears of a hard Covid lockdown sparked panic buying in Beijing on Monday, as long queues for compulsory mass testing formed in a large central district of the Chinese capital.