The COVID-19 pandemic is the most severe global emergency the World Health Organization has ever declared, the agency's chief said late on Monday night.

Six months on since the WHO declared COVID-19 a "public health emergency of international concern", Dr Tedros Adhanom Ghebreyesus has warned the world the pandemic "continues to accelerate" with the total number of cases doubling in the past six weeks. 

This is the sixth time a global health emergency has been declared under the International Health Regulations, but it is easily the most severe," he said late on Monday (NZ Time) at his daily press conference.

"Almost 16 million cases have now been reported to WHO, and more than 640,000 deaths."

"COVID-19 has changed our world. It has brought people, communities, and nations together, and driven them apart. It has shown what humans are capable of - both positively and negatively. 

Dr Ghebreyesus said when the public health emergency was declared on January 30, there were less than 100 cases recorded outside of China - where the virus originated - and no deaths.

"COVID-19 has changed our world. It has brought people, communities, and nations together, and driven them apart. It has shown what humans are capable of - both positively and negatively. 

"We have learned an enormous amount, and we’re still learning."

While nations have implemented some of the strictest lockdowns ever imposed, including requiring citizens to stay indoors and avoid travel, the WHO chief said the "fundamental pillars of the response" remain, including political leadership and engaging with communities. 

Countries continue to find, isolate, test, and care for cases, as well as tracing and quarantining their contacts.

Dr Ghebreyesus said these were the "basic measures needed to suppress transmission and save lives".

"Keep your distance from others, clean your hands, avoid crowded and enclosed areas, and wear a mask where recommended. Where these measures are followed, cases go down. Where they’re not, cases go up."

New Zealand - which currently has 21 active cases, but all of which are in quarantine facilities - was mentioned by the WHO chief for its success in fighting the SARS-CoV-2 virus.

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 "Countries and communities that have followed this advice carefully and consistently have done well, either in preventing large-scale outbreaks – like Cambodia, New Zealand, Rwanda, Thailand, Vietnam, and islands in the Pacific and Caribbean – or in bringing large outbreaks under control – like Canada, China, Germany and the Republic of Korea."

Aotearoa has recorded 1556 confirmed and probable cases of the virus overall and has virtually no restrictions remaining other than those at the border. The nearly-two-month nationwide lockdown implemented from late March has been praised for stemming the virus' spread.

"The bottom line is that one of the most fundamental ingredients for stopping this virus is determination, and the willingness to make hard choices to keep ourselves and each other safe," Dr Ghebreyesus said.

He also thanked those working for the WHO, which has come under constant attack by some politicians, including US President Donald Trump, for not scrutinising information coming out of China in the early stages of the virus' spread. The chief said the agency gave public guidance within days of learning of the virus and has never before produced such an amount of technical advice.

"We have done an incredible amount, but we still have a long, hard road ahead of us. And we know that the impacts of the pandemic are felt far beyond the suffering caused by the virus itself."

As is required under International Health Regulations, Dr Ghebreyesus said this week he would be reconvening the WHO Emergency Committee to revaluate the pandemic. 

According to Worldometers, which publishes data when it's released by individual countries rather than by the WHO, there have been 16.5 million cases of COVID-19 recorded worldwide and 653,000 deaths. More than 10.1 million people have recovered from the respiratory illness.