In his latest update, he said more than 300,000 cases of COVID-19 have now been reported to WHO, from almost every country in the world.
"It took 67 days from the first reported case to reach the first 100,000 cases, 11 days for the second 100,000 cases and just 4 days for the third 100,000 cases. You can see how the virus is accelerating."
Dr Ghebreyesus said we can change the trajectory of the pandemic but we need to do more than defensive tactics.
"Asking people to stay at home and other physical distancing measures are an important way of slowing down the spread of the virus and buying time – but they are defensive measures.
"To win, we need to attack the virus with aggressive and targeted tactics – testing every suspected case, isolating and caring for every confirmed case, and tracing and quarantining every close contact."
He said not every country has the capacity to do this but in an incredible example of international solidarity, several countries have sent emergency medical teams to care for patients and train health workers in other countries that need support.
Italy's case numbers continue to rise reaching just over 6000 deaths, followed by more than 3000 deaths in Hubei, China, the centre of the initial outbreak.
The UK and Australia have gone into lockdown.
Dr Ghebreyesus said he will be addressing heads of state and government from the G20 countries this week, asking them to work together to increase production of protective gear, life-saving tools, avoid export bans and ensure equity of distribution, on the basis of need.
In New Zealand, where there are now 155 confirmed and probable cases, the Ministry of Health has carried out more than 8000 tests for Covid-19 and the whole country will go into lockdown at alert level 4, midnight Wednesday 25 March.
"Recent travel from overseas is still the main driver of our new infections," said Director-General of Health Dr Ashley Bloomfield.
Four cases, three in Auckland and one in Wairarapa, have been classified as community spread cases.
"In these cases, we have been unable to confirm a definite link to overseas travel or to an existing confirmed case. Contact tracing is underway for all cases."
Laboratories are working as quickly as possible to process and clear test results, said Dr Bloomfield.
He said moving to alert level 4 gives New Zealand the best chance of breaking the chain of community transmission.
More restrictions around people returning to New Zealand will be announced soon, Prime Minister Jacinda Ardern told Radio NZ's Morning Report.
"Our citizens coming home are the ones carrying Covid-19."
Foreign Minister Winston Peters advised the tens of thousands of Kiwis travelling overseas to stay where they are, as many global transit routes are suspended.
"Since 18 March, we have been warning New Zealanders offshore that the window for flying home was closing," he said.