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".
At least 213 people have died in China - mostly in Hubei province where the virus emerged - 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 the Chinese city of Wuhan in Hubei.
However, there have been eight cases of human-to-human infection - in Germany, Japan, Vietnam and the United States.
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".
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:
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.
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.
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