The WHO said Monday that asking the general public to wear facemasks could be justified in areas where hand-washing and physical distancing were difficult, but warned masks alone could not stop the coronavirus pandemic.
World Health Organization chief Tedros Adhanom Ghebreyesus also slammed suggestions that Africa should be used as a testing ground for a vaccine as racist.
The global COVID-19 pandemic has killed more than 70,000 people, while more than 1.2 million people have tested positive for the new coronavirus. A vaccine is thought to be at least a year away.
"Countries could consider using masks in communities where other measures such as cleaning hands and physical distancing are harder to achieve because of lack of water or cramped living conditions," Tedros told a virtual briefing in Geneva.
Tedros said he understood that some countries had recommended or were considering the use of both medical and non-medical masks in the general population to prevent the spread of the virus.
However, he stressed that the mass use of medical masks could exacerbate the shortage of protective equipment for healthcare workers, saying some were now facing "real danger".
And he said that outside of health facilities, medical masks were recommended for those who were sick, and their carers.
- Racism row -
Tedros also lashed out at "racist" suggestions from some scientists that Africa could be used as a testing ground for a vaccine, which is thought to be 12 to 18 months away.
Two leading French doctors sparked a storm of criticism last week by discussing on television the idea of testing a coronavirus vaccine in Africa, citing its relative lack of resilience to the pandemic in its infrastructure.
They insisted Friday they had been misunderstood and apologised for any offence caused.
Africa has confirmed relatively few cases and deaths so far compared to other continents.
But the WHO and others have long warned that it could be badly exposed should the virus, both in terms of preparedness and health care.
"Africa cannot and will not be a testing ground for any vaccine," Tedros said.
"It was a disgrace, appalling, to hear during the 21st century to hear from scientists... this kind of racist remarks.
"The hang-over from the colonial mentality has to stop. WHO will not allow this to happen.
"We will follow all the rules to test any vaccine or therapeutics all over the world using exactly the same rules," said Tedros, who previously served as minister of health and foreign affairs in Ethiopia.
- Free online concert -
Meanwhile the WHO teamed up with US superstar Lady Gaga to launch a giant coronavirus awareness concert on April 18 entitled "One World: Together at Home".
The free online performances are billed as a "global broadcast and digital special to support frontline healthcare workers" and the WHO.
The gig will feature stars including Andrea Bocelli, Chris Martin, David Beckham, Elton John, John Legend, Keith Urban, Lang Lang, Paul McCartney, Priyanka Chopra Jonas, Shah Rukh Khan and Stevie Wonder.
"This global pandemic is a catastrophe," Lady Gaga said.
"We need to tell the stories of, and celebrate, the frontline community healthcare workers and their acts of kindness.
"We highlight the singular, kind global community that is arising right now."