The coronavirus outbreak is a global health emergency, the director-general of the World Health Organization has declared - but added that travel restrictions to China would be counterproductive.

An "unprecedented outbreak" had been met with an "unprecedented response", said WHO chief Tedros Adhanom Ghebreyesus, following a crisis meeting in the Swiss city of Geneva on Thursday.

More:

He called for the global community to make "evidence-based" decisions regarding travel and trade with China and decried unilateral actions to isolate Beijing, saying the WHO opposed some measures taken and threatened.

"This is the time for facts, not fear," he said. "This is the time for science, not rumours. This is the time for solidarity, not stigma."

"The Chinese government is to be congratulated," said Adhanom Ghebreyesus, "for the extraordinary measures it has taken to contain this outbreak."

The speed with which Chinese officials identified the virus, sequenced its genome and shared those findings with global public health experts was "very impressive", he added.

Public health emergency

By Thursday evening, there were 98 declared cases of coronavirus in 18 countries outside China, including eight cases of human-to-human transmission. There have so far been no deaths outside of China. More than 7,000 cases have been identified inside China, where 180 people have lost their lives.

Work to build a vaccine has already started, said the WHO head.

"We don't know what sort of damage this virus could do if it were to spread within a country with a weaker health system," said Adhanom Ghebreyesus.

"I am declaring a public health emergency of international concern."

The WHO has every confidence in China's ability to contain the outbreak and "reverse the tide", he said. He pointed to the scale of mobilisation of healthcare there, noting one hospital had been built in just 10 days.

"There is no reason for measures that affect international travel and trade," said Adhanom Ghebreyesus. "We call on all countries to implement decisions that are evidence-based and consistent."

Travel restrictions 'counterproductive'

The WHO committee said, in general, evidence has shown that restricting the movement of people and goods during public health emergencies may be ineffective and may divert resources from other interventions.

Restrictions may also interrupt needed aid and technical support, disrupt businesses, and have negative effects on the economies of countries affected by the emergencies, the WHO said in a statement.

"The only way we will defeat this outbreak," said the WHO chief, "is for all countries to work together in a spirit of solidarity and cooperation. We are all in this together, and we can only stop it together."

Some countries had taken questionable measures, said Didier Houssin, the WHO Emergency Committee chair.

"What does it mean - a travel restriction? It means, for example, visa refusal, border closure, quarantine of travellers who are in good condition," he said.

"This declaration will provide the WHO the possibility to question such measures which already have been taken by some countries: Why did you take this decision? What is the science supporting this decision? Could you reconsider this decision?

"And we suggested the WHO should inform the world about transparency concerning these measures - which should not constitute an example to follow, but a decision to reconsider."

Al Jazeera's Charlie Angela has been following the outbreak.

"There was only praise for China's response," she said. "The WHO is saying that if China hadn't responded in the way it had we would have seen many more deaths. They're saying China has done their best to contain it - but now, the WHO are taking over.

"It does seem the main concern is helping to prepare countries which, as they put it, have a weaker health system. But also they made a number of recommendations - they will not be limiting trade or travel, they're ready to give advice and support to countries, and they want to combat rumours and misinformation."

Russia on Thursday evening closed its border with China, and the WHO would now be questioning such decisions at a governmental level, Angela added.

"The declaration of the public health emergency gives them authority through the United Nations to release funding, coordinate testing and set up specialist laboratories to deal with the molecular detection of this virus," Angela noted.

But the WHO's message has not yet been acknowledged by national public health officials.

Moments after the WHO's declaration, Trinidad and Tobago imposed 14-day restrictions on travellers from China visiting the Caribbean island, while the United Kingdom announced it was raising its risk level from Coronavirus to "moderate", with the UK's Chief Medical Officers saying in a statement they considered it prudent for the government to escalate its planning in case of a more widespread outbreak.