A new strain of a deadly coronavirus has been identified in China, claiming the lives of more than 20 people and infecting hundreds more in just three weeks.
Global health authorities are now trying to coordinate their response to prevent it from spreading worldwide and avoid a repeat of the 2002 SARS outbreak, in which 774 people died.
How many people have been infected?
Between December 31 and January 22, Chinese authorities have to date diagnosed more than 600 cases of the novel coronavirus, according to France's health minister Agnès Buzyn.
Meanwhile, more than 100 people have been hospitalised with severe symptoms.
Thailand has reported two cases of the virus while Japan, South Korea and Taiwan reported one each. They all involved people who had recently visited China.
Outside of Asia, the United States also reported its first case of the virus in a patient recently returned from Wuhan, China.
Where did the virus come from?
Most cases were reported in Wuhan, a city of 11 million people in the central Chinese province of Hubei.
"The majority of detected pneumonia cases reported having visited the Wuhan Huanan Seafood Wholesale Market recently before disease onset," the European Centre for Disease Prevention and Control (ECDC) said in a statement.
It also flagged that some cases reported exposure to other markets and that a few cases had no direct connection with a market.
What are the symptoms?
This new virus can, in more severe cases, cause pneumonia, severe acute respiratory syndrome and kidney failure.
Common signs of the infection include respiratory symptoms, fever, cough, shortness of breath and breathing difficulties.
Arnaud Fontanet, a researcher from the Pasteur Institute, told AFP news agency that it is the seventh identified variety of coronavirus affecting humans. These viruses take their name from protein capsules that form a crown.
Genetically, the new virus — provisionally called "2019-nCOV" — is 80% similar to Severe Acute Respiratory Syndrome (SARS).
SARS spread rapidly in 2002 and 2003, causing nearly 800 people to die. Experts believe that this new virus is slightly weaker than SARS.
How is the virus transmitted?
"Coronaviruses are zoonotic, meaning they are transmitted between animals and people", the WHO explained in a statement.
SARS transmitted from civet cats to humans, for instance, infecting 8,000 people across 30 countries.
Meanwhile, the Middle East Respiratory Syndrome (MERS-CoV) was transmitted from dromedary camels to humans. During the 2012 outbreak, which originated in Saudi Arabia and spread to 26 countries, 567 of the more than 1,500 people infected died.
Can the virus spread worldwide?
Chinese authorities confirmed on Monday that the new strain could be transmitted from human to human, which increases the likelihood of the virus spreading.
China remains the most affected by the outbreak. Wuhan, the epicentre, has borne the brunt of it with a few cases in other major cities including Shanghai and Beijing.
But health authorities worldwide are fearful that the Chinese New Year celebrations could lead to a surge in cases internationally. Hundreds of millions of Chinese citizens travel domestically for the holiday, while millions of Chinese expatriates are expected to travel to China and could bring the virus with them when they return home.
Can Chinese data be trusted?
Scientists at the Imperial College London have expressed doubts over the veracity of the Chinese data.
They estimate that there could be as many as 1,723 cases — much higher than the more than 600 announced by Chinese authorities.
However, China's attitude towards the outbreak has been much more transparent this time than during the 2002 SARS pandemic, with authorities sharing crucial data much more quickly.
Herman Goossens from the Platform for European Preparedness Against (Re-)emerging Epidemics (PREPARE) told Euronews that China released the sequence for the virus in early January which enabled a diagnostic test to be developed.
What measures are countries taking?
There is no known vaccine for the new strain of coronavirus.
China has put three cities -Wuhan, Huanggang and Ezhou - on lockdown: stopping outbound travel in an effort to contain the virus. .
China previously disinfected the Wuhan Huanan Seafood Wholesale Market and has been carrying out temperature checks at some transport hubs.
Hong Kong authorities have been carrying such checks at the border.
Several countries including the US and Australia have also decided to carry out tests on passengers returning onboard direct flights from Wuhan.
In the EU, PREPARE has reached out to clinical sites and diagnostic labs to ensure they are ready while researchers are currently developing a clinical protocol to implement swiftly should case be reported in the bloc.
**France's health minister Agnès Buzyn said there were no cases of the virus in the country but that they did have a fast diagnostic test that could be used quickly.
"The risk is real" but "small" as there hasn't yet been a case in Europe, Buzyn said.
The World Health Organisation has been discussing this week whether or not to declare a global health emergency.