Addressing the media here on Monday, the WHO chief said: "Trust us. The worst is yet ahead of us... Let's prevent this tragedy. It's a virus that many people still don't understand," the Evening Standard newspaper reported.
"There is no secret in WHO because keeping things confidential or secret is dangerous. It's a health issue.
"This virus is dangerous. It exploits cracks between us when we have differences," he added.
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Ghebreyesus said that the US Centres for Disease Control and Prevention (CDC) staff have been seconded to work with his agency, suggesting that was a sign of the WHO's transparency.
"Having CDC staff means there is nothing hidden from the US from day one" the WHO chief said, adding: "Our CDC colleagues also know that we give information immediately to anyone."
In one of his starkest comparisons yet, the UN health agency chief also alluded to the Spanish Flu more than a century ago, reports the Evening Standard newspaper.
He said the coronavirus has a "very dangerous combination... like the 1918 flu that killed up to 100 million people".
Ghebreyesus called the illness "Public Enemy Number One" and said: "We have been warning from day one: this is a devil that everybody should fight."
As of Tuesday morning,a total of 170,324 people have so far died of the disease, while the global number of coronavirus cases stood at 2,477,426, according to the Johns Hopkins University.
The US with 42,335 deaths and 787,370 cases currently accounts for the highest number of infections and fatalities in the world.