Authorities in China are warning that the coronavirus that has killed nine people in the country is mutating and adapting.
The virus has spread from Wuhan province to Beijing to Shanghai. And cases have been detected in the US, Thailand, South Korea, Japan and Taiwan.
Some 440 cases of the virus were confirmed as of Wednesday and authorities have confirmed that it can spread through human-to-human contact.
Another 2,197 cases of close contact with patients have been confirmed.
The World Health Organisation is due to hold an emergency meeting later today to determine whether the outbreak constitutes a global health emergency.
Fifteen medical workers are among the infected in China, with symptoms including fever, breathing difficulty and coughing.
Coronaviruses are known to cause illnesses ranging from the common cold to Severe Acute Respiratory Syndrome (SARS).
The SARS outbreak that began in 2002 and 2003 killed nearly 800 people.
The Wuhan virus is known to cause pneumonia and does not respond to antibiotics.
The origin of the virus has yet to be confirmed; however, the WHO has said it is likely the primary source was probably animal. Chinese officials have linked the outbreak to Wuhan's seafood market.
Beijing has vowed to tighten containment measures in hospitals and has been providing daily updates as millions of people prepare to travel at home and abroad for the Chinese New Year.
Taiwan has joined Australia in warning citizens to avoid travel to Wuhan – and airports around the world have stepped up screening of travellers from China.