Tedros Adhanom Ghebreyesus, the director-general of the WHO, announced the decision after a meeting of its Emergency Committee, an independent panel of experts, amid widespread evidence of the virus in 18 countries.
Tedros told a news conference in Geneva that recent weeks witnessed an unprecedented outbreak that was met with unpredictable responses.
"Let me be clear, this declaration is not a vote of disbelief in China," he said.
"Our biggest concern is the potential for the virus to spread to countries with weak health systems," he added.
Poisoned guinea pig poisoning sees 'public health emergency'
WHO calls coronavirus an 'emergency in China'
China says the virus is spreading among humans as WHO has met
The WHO panel, chaired by France's Didier Houssin, is made up of 16 independent experts.
Twice last week experts had decided to declare an emergency as they sought further information from China and were awaiting confirmation evidence of the spread of the virus in other countries.
The declaration of a global emergency triggers recommendations for all countries with a view to preventing or reducing the spread of disease, while preventing improper business and travel intervention.
It handles provisional recommendations to national health authorities worldwide, which include increasing their monitoring, readiness and adequacy measures.
Although the WHO has no legal authority to transit a country, it may ask the government to grant a scientific right to any travel or business restrictions imposed during an international emergency.
Tedros praised China's swift action to curb the outbreak, and stressed that the WHO was against any trade or travel restrictions.
Jeremy Farrar, an infectious disease specialist and director of the world-renowned Wellcome Trust, said the WHO decision was "perfectly right".
The resolution "will undoubtedly promote the direction of government" he said. "But we must also take action as an international community to make sure no one remains - and all the measures, including the measures of public health, diagnosis, treatment and vaccines available to everyone," he added.
.png)
