The new coronavirus pandemic that has infected more than 16 million people is easily the worst global health emergency the World Health Organization (WHO) has faced, its director general Tedros Adhanom Ghebreyesus said on Monday.

Only with strict adherence to health measures, from wearing masks to avoiding crowds, would the world manage to beat it, Tedros added at a virtual news briefing in Geneva.

"Where these measures are followed, cases go down. Where they are not, cases go up,” he said, praising Canada, China, Germany and South Korea for controlling outbreaks.

Resurgences of the coronavirus in various regions, including where nations thought they had controlled the disease, are alarming the world, with deaths nearing 650,000.

WHO emergencies programme head Mike Ryan said far more important than definitions of second waves, new peaks and localised clusters, was the need for nations around the world to keep up strict health restrictions such as physical distancing.