WHO chief Tedros Adhanom Ghebreyesus called on countries to adopt an aggressive approach to tackling the virus, citing successful mitigation efforts in Italy, South Korea and elsewhere.
"Across all walks of life, we are all being tested to the limit," he told a virtual news conference in Geneva on Friday.
"Only aggressive action combined with national unity and global solidarity can turn this pandemic around," he added.
Elsewhere, French officials warned of rising cases in metropolitan France as the death toll there topped 30,000.
Israeli Prime Minister Benjamin Netanyahu admitted a decision to allow bars and other businesses to reopen may have come "too soon" after his country reported a record 1 500 new infections on Friday.
Australian authorities said they would slash by half the number of people allowed to return from overseas each day after a fresh surge in cases that saw a lockdown imposed on Melbourne, the country's second-largest city.
In Hong Kong, a spike has marked a setback for the city after daily life had largely returned to normal, with restaurants and bars resuming regular business and cultural attractions reopening.
Schools in the city will be closed from Monday after the city recorded "exponential growth" in locally transmitted infections.