The UK immediately increased the domestic threat level posed by coronavirus from low to moderate, saying that while it did not think the "risk to individuals" in the UK had changed, it should “plan for all eventualities”. 

Last Thursday the WHO held off calling the outbreak an emergency but since then numbers have skyrocketed, rising from some 600 confirmed cases to more than 9,600.

Finland, the Philippines and India all reported cases yesterday and the US confirmed its first cases of human to human transmission. 

While developed nations, including China, may be able to contain the spread of the virus in the short term at least, the outlook is much less clear for the mega cities of Asia and Africa.

Unlike China, the authorities in countries like India have far less central control and resources and the potential for sustained transmission is therefore much greater. There is also concern that health systems are under-resourced.

Dr Tedros emphasised that China’s response has been “unprecedented” and said the declaration of an emergency should not be interpreted as a vote of no confidence in the authorities there.

“In many ways China is setting a new standard for outbreak response,” he said. “I have never seen in my life this kind of mobilisation... which I believe will reverse the tide.” 

The WHO also warned against placing trade and travel restrictions on China such as border closures, visa restrictions and quarantines of healthy travellers, saying they were unnecessary. 

This comes as countries around the globe continue to step up containment efforts.

Russia announced on Thursday that it would close its 2,670 mile border with China and will stop issuing electronic visas to Chinese nationals, while a scheduled opening of Pakistan's snowbound land border with China on the Karakoram Highway has been postponed until April.

Six of Hong Kong’s 14 mainland crossings with China have also been sealed. 

The PHEIC is a rare classification is used to mark an “extraordinary event” that has implications for public health internationally and requires a coordinated global response. 

Declaring an emergency means the WHO can do more in terms of international coordination to control the global spread of disease.

In theory, it could also lead to a boost in funding and resources allocated by the international community to respond to the outbreak.

A public health emergency has only been declared on five other occasions - including the swine flu (H1N1) epidemic in 2009 and the ongoing Ebola outbreak in the Democratic Republic of Congo.