Wuhan, a Chinese city of nearly nine million people, is to temporarily shut public transport as it tries to halt the outbreak of a new virus.

Those living in the city have been advised not to leave, in a week when millions of Chinese are travelling for the upcoming Lunar New Year holiday.

The airport and train stations will be closed to outgoing passengers.

Bus, subway, ferry, and long-distance transport networks will shut down from 1000 local time on 23 January.

Those living in Wuhan had already been told to avoid crowds and minimise public gatherings.

Dr Tedros Ghebreyesus, the director-general of the World Health Organization, said it was a "very strong measure" that would "not only control the outbreak, they will minimise spread internationally".

Meanwhile, after a day of discussion the WHO’s emergency committee has not yet decided whether to declare a "global emergency" over the virus. Talks will continue on Thursday.

The outbreak has killed 17 people, and there are more than 500 confirmed cases.

However, calculations by scientists at the MRC Centre for Global Infectious Disease Analysis at Imperial College London suggest there are 4,000 people sick with the virus in Wuhan.

The virus originated in a seafood market that "conducted illegal transactions of wild animals", authorities said.

There is also evidence of human to human transmission with the novel virus spreading to family members and healthcare workers.

But understanding how easily and how often the virus spread between people is one of the major outstanding questions in this outbreak.

Beyond Wuhan, it has spread to several Chinese provinces, the US, Thailand, Japan and South Korea.

Late on Wednesday, Chinese authorities confirmed the number of dead had almost doubled – from nine – in the space of a day. All fatalities so far have been in Hubei, the province around Wuhan.

Officials in Hong Kong also reported the territory’s first two cases.

Known for now as 2019-nCoV, the virus is understood to be a new strain of coronavirus not previously been identified in humans. The Sars virus that killed nearly 800 people globally in the early 2000s was also a coronavirus, as is the common cold.

A global emergency is the highest level of alarm the WHO can sound and has previously been used in response to swine flu, Zika virus and Ebola.

Dr Tedros Ghebreyesus, the director-general of the WHO said more time was needed to reach a decision. "This is a complex and evolving situation," he said.

"The decision about whether or not to declare public health emergency of international concern is one I take extremely seriously and one I am only prepared to make with appropriate consideration of all the evidence," he added.

Chinese officials said the country was now at the "most critical stage" of prevention and control.

"Basically, do not go to Wuhan. And those in Wuhan please do not leave the city," said National Health Commission vice-minister Li Bin in one of the first public briefings since the beginning of the outbreak.

The virus infects the lungs and symptoms start with a fever and cough. It can progress to shortness of breath and breathing difficulties.

The first US case was confirmed on Tuesday. President Donald Trump said the situation was "totally under control" and that he trusted the information being provided by Chinese authorities.

‘Imagine shutting down London before Christmas’

By James Gallagher, BBC health and science correspondent

Wuhan is starting to look like a city in quarantine.

Officials had already warned residents not to leave the city and visitors not to come.

Now the reported public transport ban – which includes flights – slams many of the routes in and out of the city shut.

It is a significant attempt to stop the spread of this new virus, which we now know can spread from person to person.

Limiting transport will cut the chance of the virus reaching other cities in China and other countries around the world.

This all comes just as millions of people are travelling across China for the week-long holiday that is Lunar New Year.

If you’re struggling for context – imagine shutting down London in the week before Christmas.

The big question left is the roads – and whether any of Wuhan’s 8.9 million inhabitants will be able to simply drive away.

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