declared the coronavirus outbreak a pandemic on Wednesday as the disease has spread to 114 countries, killed 4,291 people, and infected more than 118,000.
"We have therefore made the assessment that COVID-19 can be characterized as a pandemic," he told reporters.
The majority of cases have been in China, the epicenter of the outbreak where more than 3,000 people have died.
Italy, the second-worst affected, has had more than 600 deaths and the entire country has been put on lockdown in a bid to contain the contagion.
Iran and South Korea have also seen infection hotspots, with more than 90 per cent of the world's cases in these four countries.
In the past two weeks, the number of cases outside China has increased 13-fold and the number of affected countries has tripled, according to the WHO.
Only 81 countries have not reported any cases, and 57 nations have seen 10 cases or less, he added.
Tedros warned that "in the days and weeks ahead, we expect to see the number of (COVID-19) cases, the number of deaths, and the number of affected countries climb even higher."
He praised China, Iran, Italy and South Korea for the measures they have taken to slow the spread of the outbreak.
Tedros criticized other nations for not doing enough to tackle the disease. "We have called every day for countries to take urgent and aggressive action. We have rung the alarm bell loud and clear."
He said that all countries "can still change the course of this pandemic."
Tedros called for widespread and coordinated efforts to tackle the crisis which he said "will touch every sector," adding that "this is not just a public health crisis."
"So, every sector and every individual must be involved in the fight," he underlined.
While the WHO has upgraded the disease to a pandemic, Tedros clarified that the situation "does not change WHO's assessment of the threat posed by this coronavirus."
"It doesn't change what WHO is doing, and it doesn't change what countries should do," he continued.
There has never been a pandemic sparked by a coronavirus before, the WHO said.