The World Health Organization (WHO) pointed Tuesday to "emerging evidence" that the coronavirus might spread by air further than previously thought, and warned the pandemic was still accelerating.

The global health body said it would put out a new scientific brief within days, after an international group of scientists concluded the virus could travel far beyond two metres (yards).

The two-metre physical distancing guideline has been a major element in the fight against COVID-19, which has killed more than 538,000 people and infected over 11.6 million since it emerged in China last December.

Meanwhile, WHO director-general Tedros Adhanom Ghebreyesus said the pandemic was showing no signs of slowing down, after 400,000 new cases were reported over the weekend.

It took 12 weeks for the world to reach the first 400,000 COVID-19 cases.

"The outbreak is accelerating and we've clearly not reached the peak of the pandemic," Tedros said.

"While the number of deaths appears to have levelled off globally, in reality some countries have made significant progress in reducing the number of deaths, while in other countries deaths are still on the rise."

The virus has "taken the world hostage", he concluded.