The new coronavirus has been declared a global emergency by the World Health Organization, as the outbreak continues to spread outside China.
"The main reason for this declaration is not what is happening in China but what is happening in other countries," said WHO chief Tedros Adhanom Ghebreyesus.
The concern is that it could spread to countries with weaker health systems.
Meanwhile, the US has told its citizens not to travel to China.
The state department issued a level four warning - having previously urged Americans to "reconsider" travel to China - and said any citizens in China "should consider departing using commercial means".
China has said it will send charter plans to bring back Hubei province residents who are overseas "as soon as possible".
A foreign ministry spokesman said this was because of the "practical difficulties" Chinese citizens have faced abroad. Hubei is where the virus emerged.
At least 213 people in the China have died from the virus, mostly in Hubei, with almost 10,000 cases nationally.
The WHO said there had been 98 cases in 18 other countries, but no deaths.
Most international cases are in people who had been to Wuhan in Hubei.
However in eight cases - in Germany, Japan, Vietnam and the United States - patients were infected by people who had travelled to China.
Speaking at a news conference in Geneva, Dr Tedros described the virus as an "unprecedented outbreak" that has been met with an "unprecedented response".
He praised the "extraordinary measures" Chinese authorities had taken, and said there was no reason to limit trade or travel to China.
"Let me be clear, this declaration is not a vote of no confidence in China," he said.
But various countries have taken steps to close borders or cancel flights, and companies like Google, Ikea, Starbucks and Tesla have closed their shops or stopped operations.
The US Commerce Secretary, Wilbur Ross, has said the outbreak could "accelerate the return of jobs to North America".
Preparing other countries
What happens if this virus finds its way into a country that cannot cope?
Many low- and middle-income countries simply lack the tools to spot or contain it. The fear is it could spread uncontrollably and that it may go unnoticed for some time.
Remember this is a disease which emerged only last month - and yet there are already almost 10,000 confirmed cases in China.
The 2014 Ebola outbreak in West Africa - the largest in human history - showed how easily poorer countries can be overwhelmed by such outbreaks.
And if novel coronavirus gets a significant foothold in such places, then it would be incredibly difficult to contain.
We are not at that stage yet - 99% of cases are in China and the WHO is convinced the country can control the outbreak there.
But declaring a global emergency allows the WHO to support lower- and middle-income countries to strengthen their disease surveillance - and prepare them for cases.
How unusual is this declaration?
The WHO declares a Public Health Emergency of International Concern when there is "an extraordinary event which is determined… to constitute a public health risk to other states through the international spread of disease".
It has previously declared five global public health emergencies:
- Swine flu, 2009 - The H1N1 virus spread across the world in 2009, with death toll estimates ranging from 123,000 to 575,400
- Polio, 2014 - Although closer than ever to eradication in 2012, polio numbers rose in 2013
- Zika, 2016 - The WHO declared Zika a public health emergency in 2016 after the disease spread rapidly through the Americas
- Ebola, 2014 and 2019 - The first emergency over the virus lasted from August 2014 to March 2016 as almost 30,000 people were infected and more than 11,000 died in West Africa. A second emergency was declared last year as an outbreak spread in DR Congo
How is China handling the outbreak?
A confirmed case in Tibet means the virus has reached every region in mainland China. According to the country's National Health Commission, 9,692 cases have tested positive.
The central province of Hubei, where nearly all deaths have occurred, is in a state of lockdown. The province of 60 million people is home to Wuhan, the heart of the outbreak.
The city has effectively been sealed off and China has put numerous transport restrictions in place to curb the spread of the virus.
People who have been in Hubei are also being told to work from home until it is considered safe for them to return.
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.
How is the world responding?
Voluntary evacuations of hundreds of foreign nationals from Wuhan are under way.
The UK, Australia, South Korea, Singapore and New Zealand are expected to quarantine all evacuees for two weeks to monitor them for symptoms and avoid contagion.
Australia plans to quarantine its evacuees on Christmas Island, 2,000km (1,200 miles) from the mainland in a detention centre that has been used to house asylum seekers.
In other recent developments:
- Italy suspended flights to China after two Chinese tourists in Rome were diagnosed with the virus; earlier 6,000 people on board a cruise ship were temporarily barred from disembarking
- In the US, Chicago health officials have reported the first US case of human-to-human transmission. Around 200 US citizens have been flown out of Wuhan and are being isolated at a Californian military base for at least 72 hours
- Russia has decided to close its 4,300km (2,670-mile) far-eastern border with China
- Two flights to Japan have already landed in Tokyo. Japan has now raised its infectious disease advisory level for China
- Some 250 French nationals have been evacuated from Wuhan
- India has confirmed its first case of the virus - a student in the southern state of Kerala who was studying in Wuhan
- Israel has barred all flight connections with China
- Papua New Guinea has banned all visitors from "Asian ports"
- North Korea will suspend all flights and trains to and from China, said the British ambassador to North Korea
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