Coronavirus has spread to more than 110 countries, including the UK, and claimed more than 4,600 lives.
So, what is the disease and how does it spread?How do I protect myself?
The best thing is regular and thorough hand washing, preferably with soap and water.
Coronavirus spreads when an infected person coughs small droplets - packed with the virus - into the air. These can be breathed in, or cause an infection if you touch a surface they have landed on then your eyes, nose or mouth.
So, coughing and sneezing into tissues, not touching your face with unwashed hands, and avoiding close contact with infected people are important for limiting the spread.
Face masks do not provide effective protection, according to medical experts.
What are the coronavirus symptoms?Coronavirus infects the lungs. The symptoms start with a fever followed by a dry cough, which can lead to breathing problems.
It takes five days on average to start showing the symptoms, scientists have said, but some people will get symptoms much later than this.
The incubation period lasts up to 14 days, the World Health Organization (WHO) says. But some researchers say it may be up to 24 days.
People will be most infectious when they have symptoms, but there have been suggestions some can spread the virus even before they are sick.
The early symptoms can easily be confused with other winter bugs including colds and flu.
How deadly is coronavirus?
The proportion dying from the disease appears low (between 1% and 2%) - but the figures are unreliable.
Thousands are being treated but may go on to die - so the death rate could be higher. But it may also be lower if lots of mild cases are unreported.
A World Health Organization examination of data from 56,000 patients suggests:
6% become critically ill - lung failure, septic shock, organ failure and risk of death
14% develop severe symptoms - difficulty breathing and shortness of breath
80% develop mild symptoms - fever and cough and some may have pneumonia
Older people, and those with pre-existing medical conditions (such as asthma, diabetes, heart disease, high blood pressure), are more likely to become severely ill. The data from China also suggests that men are at slightly higher risk of dying from the virus than women.
Treatment relies on keeping the patient's body going, including breathing support, until their immune system can fight off the virus. Work to develop a vaccine is under way.
What should I do if I think I have coronavirus?
The NHS says an epidemic in the UK is "likely".
Patients with mild symptoms - such as a new continuous cough or a high temperature above 37.8C- should self-isolate at home for at least seven days, according to the latest advice issued by Public Health England on Friday.
Community teams will keep an eye on them if need be.
But people are being advised not to ring NHS 111 to report their symptoms unless they are worried. They should also not go to their GP, or A&E. Details for Scotland are to check NHS inform, then ring your GP in office hours, or 111 out-of-hours. In Wales call NHS 111, and in Northern Ireland, call your GP.
If you have come into contact with somebody who may be infected, you may be told to self-isolate. People needing to do so should take "common-sense" steps to avoid close contact with other people, says Public Health England.
Advice for people who have travelled back to the UK from affected areas and who may need to self-isolate, has been issued.
Other countries have introduced their own measures For example, the US Centers for Disease Control and Prevention advises people showing symptoms to call their healthcare provider, and those who are mildly ill to self-isolate.
The World Health Organization has also issued advice for the public.
Who gets tested and how does it work?
People showing symptoms who call 111 who have been to one of the affected areas, or who have been in close contact with someone who has the virus, will be tested.
All hospital patients with flu-like symptoms will also be tested.
If you need testing in the UK, you may have to give samples of mucus, blood or faeces. These will be tested and results may be available on the same day.
While you await your test results, you may be asked to stay at home and self-isolate.
How fast is it spreading?
Hundreds of new cases are being reported worldwide each day. However, it is thought health agencies may be unaware of many cases.
After starting in China, coronavirus is now spreading fast in countries like South Korea, Italy and Iran.