The World Health Organization is alerted by the Chinese authorities to a string of pneumonia-like cases in Wuhan, a city of 11 million people.
Patients are quarantined and work begins on identifying the origin of the pneumonia.
The US Centers for Disease Control and Prevention identifies a seafood market believed to be at the centre of the outbreak. It is closed on 1 January.
The WHO says the outbreak in Wuhan was caused by a previously unknown type of coronavirus, which is a broad family ranging from the common cold to more serious illnesses like SARS.
China says a first person has died of the virus
The virus spreads beyond China's borders for the first time with a case emerging in Thailand, according to the WHO.
The victim is a Chinese woman diagnosed with mild pneumonia returning from a trip to Wuhan.
China's health commission says no human-to-human transmission of the virus behind the Wuhan outbreak has been confirmed so far but the possibility "cannot be excluded".
A first case of the virus is confirmed in Japan in someone who had stayed in Wuhan in early January.
A second person, a 69-year-old man, dies in Wuhan and the CDC says it will begin screening passengers arriving from Wuhan at three airports: San Francisco, New York's JFK and Los Angeles.
A third death and more than 100 new cases are announced in China, sparking concerns ahead of the annual Lunar New Year holiday from 25 January, which sees hundreds of millions of Chinese people travel nationwide.
The virus is present in Beijing in the north, Shanghai in the east and Shenzhen in the south with more than 200 cases recorded. The virus is also detected in South Korea in a Chinese person who flew in from Wuhan.
Human-to-human transmission is "affirmative", a top Chinese expert on infectious diseases Zhong Nanshan tells state broadcaster CCTV.
The first case is announced in the United States.
Trains and planes are no longer running in Wuhan and New Year festivities are scrapped in Beijing as the WHO declares an emergency.
China reports two deaths far from Wuhan and France confirms three cases, Europe's first.
Beijing orders control measures on public transport -- Hubei province is all but cut off with more than 56 million residents confined indoors. Hong Kong declares a maximum health alert.
The next two days see Beijing suspend trips organised both at home and abroad and the first death in the capital. Germany and the United States advise against travel to China.
Germany and Japan announce the first cases of direct transmission outside China. The US begins development of potential vaccines.
Total registered infections surpass those of SARS as the first cases emerge in the Middle East. The WHO urges a global response.
The world indoor athletics championships scheduled for March in Nanjing are pushed back to next year and many sports events are cancelled. The Chinese football league is suspended.
Japan and the United States begin repatriations as airlines begin suspending flights to China.
Several foreign companies in the world's third-biggest consumer market say they are suspending operations. Apple announces temporary closures of its Chinese stores.
As France announces a sixth case, Russia says it will close its border with China.
The WHO declares a global virus emergency with the death toll having passed 200. In Britain, the first UK cases of the virus are confirmed, while Italy declared a state of emergency.
The EU says it is earmarking €10m for research. The Pasteur Institute in Paris, along with Chinese and Australian researchers, isolates the virus culture, a major step towards eventual production of a vaccine.
The official toll stands at 304 deaths for more than 14,000 confirmed cases. Wenzhou, a city of nine million 800km from Wuhan, becomes the second city to be locked down.
Meanwhile, the WHO says the Philippines has reported the first virus death to occur outside China, a man from Wuhan.