China’s mystery new coronavirus has so far infected more than 830 people and killed 25.
While the vast bulk of cases have been confined to China, cases in this fast-moving outbreak have now been found in the United States, Hong Kong, Thailand, South Korea, Taiwan, Macau, Japan and the Philippines. Fourteen people are being tested in the United Kingdom.
And experts the world over are on high alert after authorities confirmed that the virus could jump from human to human.
The World Health Organisation said it is "too early" to declare an international public health emergency over the outbreak "given its restrictive and binary nature".
Speaking at a press conference, Dr Tedros Adhanom Ghebreyesus, director-general of the WHO, said: "Make no mistake, this is though an emergency in China.
"But it has not yet become a global health emergency. It may yet become one."
Athough it remains unlikely that the outbreak will grow into a global epidemic, experts have been warning for years that the world is long overdue a major disease outbreak.
And so it is sensible to be prepared. This guide will be updated daily and is underpinned with the best advice from leading experts from the NHS and beyond.
What are the symptoms of the new coronavirus?
According to the WHO, the new coronavirus causes a fever, fatigue, sore throat and dry cough in the early stages of the disease. As the illness progresses, patients may experience difficulty breathing.
But these symptoms – similar to many other respiratory diseases – are what make it so difficult to control.
The virus was initially described by Chinese authorities as a new strain of pneumonia, but was later confirmed to be a novel coronavirus.
These are a family of viruses that originate in animals before making the jump to humans. Seven, including the new virus, have been found in humans, with four causing only mild, common-cold like symptoms.
But two – Middle East respiratory syndrome (Mers) and severe acute respiratory syndrome (Sars) – are much more severe, having killed more than 1,500 people between them.
Around 15 to 20 per cent of hospital cases are severe and the current death rate stands at about two per cent. This is quite high but it may be because authorities are not aware of milder cases of the disease.
How are coronaviruses transmitted?
Like other coronaviruses – such as the common cold – the virus is spread via droplets when a person coughs or sneezes. It can also be spread when someone touches a contaminated surface such as a door handle.
Hospitals are also key locations for "super spreading" events - when a single patient infects many people. When patients arrive in hospital with vague respiratory symptoms health workers may not know they need to take special precautions such as wearing masks or keeping them away from other patients.
The outbreak originates from animals and the source is thought is thought to be a seafood market in Wuhan which also traded in other live animals such as marmots and bats.
Can the new coronavirus be treated?
There are no specific treatments for coronaviruses – just as there is no treatment for the common cold.
Peter Horby, professor of emerging infectious diseases and global health, at the Centre of Tropical Medicine and Global Health at the University of Oxford, said the disease bore all the signs of a "classic viral pneumonia".
"There are currently no antivirals for this, so care is just supportive, supporting the lungs and other organs until patients recover," he said.
"There are other potential therapeutics out there but no effective antiviral," he added.
According to CNN, researchers in the US and China have already begun working on a vaccine, thanks to China's prompt sharing of the virus's genetic code.
However, any vaccine will not be available for up to a year and would most likely be given to health workers most at risk of contracting the virus.
What can you do to limit the risk of catching the new coronavirus?
The risk to the UK is currently low. But anyone travelling to China and worried about catching the virus needs to take the basic hygiene precautions.
Maria Van Kerkhove, acting head of emerging infectious diseases at the WHO, said: “Coronaviruses typically cause respiratory symptoms so we recommend basic hand hygiene such as washing hands in soap and water and respiratory hygiene so when you sneeze, sneeze into your elbow.”
She cautioned against any unnecessary contact with live animals in China.
Nick Phin, deputy director of the National Infection Service at Public Health England, added: “Individuals should seek medical attention if they develop respiratory symptoms within 14 days of visiting Wuhan, either in China or on their return to the UK, informing their health service prior to their attendance about their recent travel to the city.”
What advice has the UK government issued?
The government has not issued any travel or trade restrictions with China and says the risk to the UK is currently low and even the risk to travellers to Wuhan – a city of 11 million people – is also low.
However, it says its advice is constantly under review.
Travellers arriving on flights at Heathrow from Wuhan will be separated from other passengers and Public Health England has announced "enhanced monitoring of direct flights" and health workers on site to greet incoming flights from Wuhan.
Have international travel warnings been issued?
The European Centre for Disease Control (ECDC) increased its risk assessment on Tuesday, saying that there is now a “moderate” chance the virus could reach the European Union.
Three airports in the EU have direct flight connections to Wuhan – including London Heathrow.
But the risk of international transmission remains highest in Asia, where cases have already crossed borders. Tighter screening measures have been introduced at airports across the continent, as well as in Australia, New Zealand and at three major transit hubs in the United States.
But screening cannot pick up everyone as the incubation period for contracting the virus and the onset of symptoms is between six to 10 days.
Professor David Heymann, infectious diseases expert at the London School of Hygiene and Tropical Medicine, said: “Temperature screening picks up people with fevers – but people can take aspirin if they want to travel and don’t want to get picked up. The best thing to do is educate people – if you’re sick you should tell a doctor,” he said.
Are certain groups more at risk?
At least two of the deaths have been in people with underlying conditions and older people seem to be more vulnerable to the most severe form of the disease.
But information filtering out of China and other countries suggests that people of all ages are at risk of contracting the disease. Wuhan's health commission said in a statement that the 60 most recent cases range in age from 15 to 88.
What is the difference between a coronavirus and a flu virus?
Coronaviruses and flu viruses might cause similar symptoms but genetically they are very different.
“Flu viruses incubate very rapidly - you tend to get symptoms two to three days after being infected, but coronaviruses take much longer, ” said Professor Neil Ferguson, a disease outbreak scientist at Imperial College London.
“[With the] flu virus you become immune but there are lots of different viruses circulating. Coronaviruses don’t evolve in the same way as flu with lots of different strains, but equally our body doesn’t generate very good immunity,” he added.
What risks are presented if the coronavirus mutates?
Chinese officials have warned that the virus is already starting to mutate, which means there's a chance that the disease could start to infect many more people.
“The worry is that if you have a new virus that is exploring a human host it’s possible that they might mutate and spread more easily in humans,” Jonathan Ball, professor of molecular virology at the University of Nottingham, told The Telegraph.
The genetic sequence of the virus shows a slow mutation rate, said Prof Ferguson.
"Could it mutate to become more lethal and transmissible? That’s speculation," he said.
How does this coronavirus compare to past respiratory pandemics?
The 1918 Spanish Influenza - or H1N1 virus - remains the most devastating flu pandemic in modern history. The disease swept around the globe and is estimated to have caused between 50 and 100 million deaths.
The same virus was also behind the 2009 swine flu outbreak, which is thought to have killed as many as 575,400 people.
Other major influenza outbreaks include the Asian flu in 1957, which led to roughly two million deaths, and the Hong Kong flu 11 years later which killed one million people.
But coronavirus outbreaks have been far smaller. Sars eventually spread to 27 countries in total, infecting around 8,000 people and killing 700.
Mers on the other hand has proved less explosive but more tenacious - it first emerged in 2012 in Jordan, when it jumped from camels to humans, and then spread throughout the Arabian peninsula.
Around 2,500 cases of the disease have been identified so far and, while the disease hit a peak of more than 600 cases in 2014, there were still more than 190 cases last year. It is more deadly than Sars, and has claimed around 850 lives in total.