Ghebreyesus gave the advice in a speech read at a news conference in Geneva, posted on the agency’s website.
The director-general said that no fewer than 16,000 lives had been lost to the virus.
“We know we will lose more – how many more will be determined by the decisions we make and the actions we take now.
“To slow the spread of COVID-19, many countries have introduced unprecedented measures, at a significant social and economic cost. They have closed schools and businesses, cancelled sporting events and asked people to stay home and stay safe.