The World Health Organisation has declared the coronavirus outbreak in China a public health emergency of international concern.

Photo: AFP

Tedros Adhanom Ghebreyesus, WHO director-general, announced the decision after a meeting of independent panel of experts, amid mounting evidence of the virus spread to some 18 countries.

He said the greatest concern was the potential for the virus to spread to countries with weaker health systems.

The outbreak has killed 170 people in China where the virus originated in an illegal wildlife market in the city of Wuhan.

The vast majority of the more than 8100 cases detected globally have been in China, but more than 100 cases have emerged in other countries, from Japan to the United States.

"Let me be clear, this declaration is not a vote of no-confidence in China," Tedros said.

Tedros praised the "extraordinary measures" taken by China taken to prevent the new virus from spreading.

Coronavirus was an "unprecedented outbreak" that had been met with an "unprecedented response", he said.

Tedros reiterated the WHO was not recommending any trade or travel restrictions to China.

What does the declaration mean?

The WHO panel, chaired by Didier Houssin of France, is composed of 16 independent experts.

Twice last week the experts had decided not to declare an emergency while they sought more information from China and awaited evidence of confirmed person-to-person spread of the virus in other countries, so as to meet their criteria for a global emergency.

The declaration of a global emergency triggers recommendations to all countries aimed at preventing or reducing cross-border spread of disease, while avoiding unnecessary interference with trade and travel.

It covers temporary recommendations for national health authorities worldwide, which include stepping up their monitoring, preparedness and containment measures.

Although the WHO has no legal authority to sanction countries, it could ask governments to provide scientific justification for any travel or trade restrictions that they impose in the event of an international emergency.

The BBC reported the WHO will now be able to support lower and middle income countries, helping them strengthen their disease surveillance and prepare them for possible cases.

University of Otago epidemiologist Professor Michael Baker told Morning Report the declaration would be a signal that more coordination was needed between countries.

"It also means they'll put much more effort into formulating international regulations and recommendations on how to contain it and I think will strengthen the hand of countries to do more at borders.

When have global health emergencies been declared before?

The WHO has previously declared five global public health emergencies:

Swine flu, 2009 - The H1N1 virus spread across the world in 2009, killing more than 200,000 people, and a public health emergency was called to ensure the world was carefully monitoring its spread and able to respond, including with vaccines.

Polio, 2014 - Although closer than ever to eradication in 2012, polio numbers rose in 2013. An emergency was declared due to fears the global fight against its eradication could face a major setback.

Zika, 2016 - The WHO declared Zika a public health emergency in 2016 after the disease spread rapidly through the Americas. Although for many Zika symptoms are mild, it can be dangerous for pregnant women and the emergency was called to spur urgent research.

Ebola, 2014 and 2019 - The deadly disease has twice been declared a public health emergency. The first one lasted from August 2014 to March 2016 as almost 30,000 people were infected and more than 11,000 died in West Africa. The WHO cited "the virulence of the virus, the intensive community and health facility transmission patterns, and the weak health systems" in affected countries. A second emergency was declared last year as the disease spread in the DR Congo.

Travel, trade

The WHO said it was not recommending limiting trade or travel to China.

The virus is affecting China's economy, the world's second-largest, with a growing number of countries advising their citizens to avoid all non-essential travel to the country.

That includes New Zealand which is advising against non-essential travel, and Australia, which is urging citizens to "reconsider" their need to travel there while the outbreak is ongoing.

Several international airlines have stopped or scaled back their routes to China and companies like Google, Ikea, Starbucks and Tesla have closed their shops or stopped operations.

When the WHO declared the Ebola outbreak in the Democratic Republic of the Congo (DRC) an emergency last year, the director-general warned countries against using it as "an excuse to impose trade or travel restrictions".

The cost to the world economy of the 2002-2003 SARS epidemic was estimated at $US33 billion. SARS - another form of coronavirus - claimed the lives of more than 700 people and infected more than 8,000.

- Reuters / BBC / ABC