GENEVA (AFP) -- The UN health agency on Thursday declared an international emergency over the deadly novel coronavirus from China -- a rarely used designation that could lead to improved international co-ordination in tackling the disease.

"Our greatest concern is the potential for the virus to spread to countries with weaker health systems," World Health Organization (WHO) chief Tedros Adhanom Ghebreyesus said as he declared a "public health emergency of international concern".

"This is not a vote of no confidence in China," he said, emphasising repeatedly that the measure was intended to help other countries less able to cope and praising the Chinese government for taking swift action to tackle the outbreak.

"We must all act together now to limit further spread.... We can only stop it together," said Tedros, who travelled to China this week and met with President Xi Jinping.

Tedros also said there was "no reason" for any of the international travel or trade restrictions announced in recent days, such as flight suspensions, border closures and quarantine for apparently healthy travellers.

Top airlines including Air France, British Airways and Lufthansa have suspended or cut back services to China.

The WHO's Emergency Committee, an advisory body of international experts, said in a statement that evidence had shown that restricting movement of people and goods during public health emergencies "may be ineffective and may divert resources from other interventions".

"Further, restrictions may interrupt needed aid and technical support, may disrupt businesses, and may have negative effects on the economies of countries affected by the emergencies," the committee said.

But it added that "in certain specific circumstances, measures that restrict the movement of people may prove temporarily useful" -- a possible reference to lockdowns within China that have affected millions of people.

WHO stopped short of declaring an emergency last week because its emergency committee was divided over the issue.

More than 7,700 people have been infected with the virus -- almost all of them in China -- and 170 have died.

The WHO said there have also been 82 confirmed cases in 18 other countries, including cases of onward transmission in Germany, Japan, the United States and Vietnam.

The WHO has called a public health emergency of international concern only five times since the relevant legislation took effect in 2007 -- for swine flu, polio, Zika and twice for Ebola outbreaks in Africa.

The designation, which is reviewed every three months, allows the WHO to issue global recommendations that the international community is expected to follow.

Governments, companies and people around the world have already been escalating efforts to contain the illness, which is believed to have emerged from an animal market in the central Chinese city of Wuhan.

Many countries have urged their citizens not to visit China, while some have banned entry for travellers from Wuhan and Russia said it was closing its far eastern border with China over the outbreak. (AFP)