He called on countries to introduce rigorous testing and contact-tracing strategies.
But he said that "there is now no treatment that has been proven to be effective against Covid-19", and warned against the use of drugs not shown to work against the disease.
The organisation's director-general, Tedros Adhanom Ghebreyesus, said during a virtual briefing that contrary to what people may believe, young people are "not invincible", and that even if you do not get sick, "the choices you make about where you go could be the difference between life and death for someone else".
The number of officially recorded cases is believed to represent only a fraction of the true number of infections, with many countries only testing the most severe cases in need of hospitalisation.
On Monday afternoon, Italy said 6,077 people in the country have now died from COVID-19, and the country confirmed almost 64,000 cases in total.
World Health Organization said that it's still possible to change the direction of the outbreak but only if nations attack now.
Tedros also said that those materials must be distributed fairly and arrive where they are needed most.
He praised countries for mobilizing their resources and sending emergency medical teams and supplies to help other crisis-hit nations, and urged the WHO's partners and nations around the world to "rationalise and prioritize" the use of personal protective equipment and cooperate to ease these issues.
He described them as "defensive measures that will not help us to win".
Health leaders were also asked about the possibility of a loss of taste and smell being a symptom of Covid-19. With masks, ventilators and political goodwill in desperately short supply, more than one-fifth of the worlds population was ordered or urged to stay in their homes Monday at the start of what could be a pivotal week in the battle to contain the Coronavirus in the U.S. and Europe.
He also said that several people are now involved in finding a vaccine and of drugs to treat COVID-19.
Tedros said so far 10 million people have signed up for the WHO's English health alert message service on WhatsApp, with versions in Arabic, French and Spanish this week.
"The future of this pandemic to a greater extent will be determined by what happens with very large, densely populated countries", Ryan said.
"The decision to postpone the games would be purely a decision of the Japanese Government and the International Olympic Committee but we are in the process of offering them risk advice".