Chinese President Xi Jinping has held a special government meeting on the Lunar New Year public holiday to warn that the spread of a deadly new virus is “accelerating”.
The country is facing a “grave situation” Mr Xi told senior officials, according to state television.
The coronavirus has killed at least 41 people and infected almost 1,300 since its discovery in the city of Wuhan.
Travel restrictions have already hit several affected cities.
And from Sunday, private vehicles will be banned from the central districts of Wuhan, the source of the outbreak.
A second emergency hospital is to be built there within weeks to handle 1,300 new patients, and will be finished in half a month, state newspaper the People’s Daily said. It is the second such rapid construction project: work on another 1,000-bed hospital has already begun.
Specialist military medical teams have also been flown into Hubei province, where Wuhan is located.
The urgency reflects concern both within China and elsewhere about the spread of the virus which first appeared in December.
Lunar New Year celebrations for the year of the rat, which began on Saturday, have been cancelled in many Chinese cities.
Across mainland China, travellers are having their temperatures checked for signs of fever, and train stations have been shut in several cities.
In Hong Kong, the highest level of emergency has been declared and school holidays extended.
Several other nations are each dealing with a handful of cases, with patients being treated in isolation.
What is the coronavirus, and what does it do?
A coronavirus is a family of viruses which include the common cold.
But this virus has never been seen before, so it’s been called 2019-nCov, for “novel coronavirus”.
New viruses can become common in humans after jumping across the species barrier from animals.
The Sars [Severe Acute Respiratory Syndrome] outbreak of 2003 started in bats and transferred to the civet cat which passed it on to humans.
This new virus also causes severe acute respiratory infection.
Symptoms seem to start with a fever, followed by a dry cough and then, after a week, lead to shortness of breath and some patients needing hospital treatment.
There is no specific cure or vaccine.
Based on early information, it is believed that only a quarter of infected cases are “severe”, and the dead are mostly – though not exclusively – older people, some of whom have pre-existing conditions.
What’s happening at the source?
The city of Wuhan is effectively on lockdown, with heavy restrictions on travel in and out, and public transport options from buses to planes cancelled.
It is a major population centre with up to 11 million inhabitants – comparable in size to London.
Pharmacies in the city have begun to run out of supplies and hospitals have been filled with nervous members of the public.
But even for those free of infection, there has been an impact on daily life, as officials have urged people to avoid crowds and gatherings.
“The whole transport system has been shut down,” Kathleen Bell, who is is originally from the UK and works in Wuhan, told the BBC. “From midnight tonight private cars are not allowed on the road. And taxis aren’t running.”
“You have queues of people lining up to be seen, some may not have the virus, and some may, and they’re all in the same space,” she said.
Major Western brands such as McDonald’s and Starbucks have closed in the city and in others nearby.
“The streets are pretty much empty,” said Mustafa Siddiqui, a businessman in Wuhan. “No-one’s going outside.”
“There’s no real panic. There is calm. There is nothing really happening.”
The surrounding Hubei province is also deeply affected, with nearly a dozen cities enduring some sort of travel restriction.
Where has it spread?
There are now nearly 1,300 confirmed cases all across China, though most concentrated in those closest to Hubei.
But it has also spread abroad – in isolated cases affecting small numbers of patients.
On Saturday, Australia confirmed its first four cases – first in Melbourne, and then three more in Sydney.
It has also spread to Europe, with three cases confirmed in France. The UK is investigating a number of suspected cases, with officials trying to trace around 2,000 people who have recently flown to the UK from Hubei province.
The cases largely involve people who had recently travelled from the affected region in China.
China’s neighbours in the Asia region are on high alert, however, with cases reported in Thailand, Singapore, Japan, Taiwan, Malaysia, Vietnam, South Korea and Nepal.
There are also cases in the United States.