The United Nations health agency’s ruling came on the same day that the Chinese government placed eight cities in central China’s Hubei province, including its capital Wuhan, under near-lockdown to stop the virus from spreading, blocking off all outward public transport. More than 800 cases worldwide have been reported so far.

The WHO’s emergency committee was almost equally divided over whether to declare the outbreak a “public health emergency of international concern”, said the panel’s chair, Didier Houssin.

Several of the committee’s 21 members indicated they believed it was “too early” to declare an emergency because of the limited number of cases outside China.

The panel would reconvene at any time – “even in the coming days” – should it be deemed necessary for it to revisit its decision, Houssin said.

Though it did not announce an emergency, the body called for a number of measures in response to the outbreak, including forming an international, multidisciplinary mission to investigate “the unknowns” of the epidemic, Houssin said. Such unknowns included the animal source of the contagion and the mode of transmission.

The WHO was also putting together a “technical package” of advice for all countries, said Maria Van Kerkhove, a committee member and head of the outbreak investigation task force at the Pasteur Institute’s Centre for Global Health in Paris.

Such recommendations centred on the need to identify cases early, prevent human-to-human transmission and provide appropriate care for those who had been diagnosed, she said.

Since the virus first came to the attention of Wuhan’s health authorities late last year, the coronavirus has spread to multiple major cities across China, several East and Southeast Asian countries, and even the US west coast.

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Despite the contagion’s increasing reach, the WHO did not recommend any further restrictions on travel or trade, said Tedros. Earlier in the day, the US state department warned China-bound travellers to exercise “increased caution”, recommending they avoid all animals, alive or dead, stay away from animal markets and avoid contact with sick people in the country.

Speaking to reporters in Washington on Thursday, a White House spokesman said that US President Donald Trump had been briefed on the virus outbreak and remained “consistently vigilant in making sure that this doesn’t spread throughout our country”.

Vietnam and Singapore reported their first cases of the virus on Thursday, bringing the global total to 647. At least 632 cases are in China, and mostly concentrated in Wuhan.

Known as 2019-nCoV, the virus is thought to have been first contracted by humans at a seafood and meat market in the city, a major transport hub connected to much of China through high-speed rail networks and flight routes.

WHO officials would not say on Thursday whether they approved of Chinese authorities’ decision to put Wuhan under quarantine, but called on the government to ensure that emergency measures were kept as brief as possible.

“China is a sovereign nation with the autonomy to take steps it believes are in its interest and that of its people,” Tedros said. “China has taken measures which it believes will be effective. But we hope from our side that they’re both effective and short in duration.”

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Late on Thursday, the Chinese government also announced that the ministry of finance was releasing 1 billion yuan (US$144 million) of emergency funds to “support Hubei province in carrying out its work to prevent and control the epidemic”.

In tackling the epidemic, the Chinese government should “pursue its policy of transparency” in sharing data with global partners, and provide “all explanations about risk management”, as well as the reasons for and means by which any measures are taken, Houssin said.

Efforts to contain the virus have been complicated by numerous factors, including the outbreak’s coinciding with the Lunar New Year holiday, when much of the country travels to visit family.

Health authorities were in a better position to combat the Wuhan coronavirus compared with similar past outbreaks because the current virus had been identified relatively quickly and could be readily diagnosed, said Michael Ryan, executive director of the WHO’s health emergencies programme.

“There are many things that are giving us an advantage, but our disadvantage is the unknowns, in not fully understanding the disease, not fully understanding its severity, not fully understanding its transmission,” he said.

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Fatality rates for 2019-nCoV are currently lower than those for severe acute respiratory syndrome (Sars) and Middle East respiratory syndrome (Mers), two other forms of coronavirus that caused hundreds of deaths during outbreaks in the early 2000s and mid-2010s, respectively.

But Ryan warned against making any pronouncements about the “true severity” of an epidemic during its early stages.

“The outbreak is still evolving,” he said. “We’re not in a position to say the epidemic has peaked.”

Chinese health authorities said on Thursday that the elderly were most susceptible to the new virus, after it emerged that half of those who died were over 80 and most had pre-existing conditions.