More than 18.14 million people around the world are reported to have been infected with the disease and 688,080 have died, according to a Reuters tally.

WHO Director-General Tedros Adhanom Ghebreyesus and WHO emergencies head Mike Ryan exhorted all nations to rigorously enforce health measures such as mask-wearing, social distancing, hand-washing and testing.

"The message to people and governments is clear: 'Do it all'," Tedros told a virtual news briefing from the UN body's headquarters in Geneva. He said face masks should become a symbol of solidarity round the world.

"A number of vaccines are now in phase three clinical trials and we all hope to have a number of effective vaccines that can help prevent people from infection. However, there's no silver bullet at the moment - and there might never be."

Ryan said countries with high transmission rates, including Brazil and India, needed to brace for a big battle: "The way out is long and requires a sustained commitment."

The WHO officials said an advance investigative team in China, where the virus originated, was not yet back.

A larger, WHO-led team of Chinese and international experts is planned next to study the origins of the virus in the city of Wuhan, although the timing and composition of that is not yet clear.

Tedros also urged mothers to continue breastfeeding even if they had COVID-19, as the benefits "substantially" outweighed the risks of infection.

Australian Associated Press