The coronavirus has now killed 25 people in China and infected more than 800.
Most of the cases are in the central Chinese city of Wuhan, where the virus is believed to have originated late last year.
But non-fatal cases have been found in at least seven other countries, including the United States.
The World Health Organisation declared it an emergency but stopped short of declaring the epidemic of international concern.
In the UK, 14 people have been tested for the deadly virus.
Five returned negative results and nine were still waiting to find out if they had been infected, Public Health England (PHE) said on Thursday night.
Health officials fear the transmission rate could accelerate as hundreds of millions of Chinese travel at home and abroad during week-long holidays for the Lunar New Year, which begins on Saturday.
But it was a "bit too early" to consider the outbreak a "Public Health Emergency of International Concern," WHO Emergency Committee panel chair Didier Houssin said after the body met in Geneva.
Such a designation would have required countries to step up the international response.
"Make no mistake, though, this is an emergency in China," said WHO chief Tedros Adhanom Ghebreyesus.
"It has not yet become a global health emergency. It may yet become one," he said.
Scrambling to contain the outbreak, the local government in Wuhan, a city of 11 million people in Hubei province, suspended most transport on Thursday, including outgoing flights, and people were told not to leave. Hours later, neighbouring Huanggang, a city of about seven million people, announced similar measures.
China later broadened the lockdowns to new cities, encompassing more than 20.5 million people, to try to contain new virus.
The previously unknown virus strain is believed to have emerged from illegally traded wildlife at an animal market in Wuhan.
It has created alarm because there are a number of unknowns surrounding it.
There is no vaccine for the virus, which can spread through respiratory transmission. Symptoms include fever, difficulty breathing and coughing.
