China virus: three weeks of growing alarm

• On December 31 China alerts the World Health Organization (WHO) to several cases of pneumonia in Wuhan.
• China announces on January 11 its first death, that of a 61-year-old man.

Here is a timeline.

Alarm raised

On December 31 China alerts the World Health Organization (WHO) to several cases of pneumonia in Wuhan, a port city of 11 million people in Hubei province. The virus is unknown.

Several of the ill worked at the city's Huanan Seafood Wholesale Market, which is shut down on January 1.

As experts work on identifying the virus, the number of infections exceeds 40.

New coronavirus

On January 5, Chinese officials rule out the SARS virus -- an illness that originated in China and killed more than 770 people worldwide over 2002-2003.

On January 7, they announce they have identified a new virus, the WHO reports. It is from the coronavirus family, which includes SARS and the common cold, and is named 2019-nCoV.

First death

China announces on January 11 its first death, that of a 61-year-old man who had purchased goods from the Wuhan market.

Other countries

On January 13, the WHO reports a case in Thailand, the first outside of China, of a woman who had arrived from Wuhan.

On January 16 Japan's health ministry reports a confirmed case of a man who had also visited the city.

The following day, as a second death is reported in Wuhan, US health authorities announce the start of screening at three airports of passengers arriving from the city.

Human transmission confirmed

On January 20 China reports a third death and more than 200 infections, with cases also reported outside Hubei province including in Beijing, Shanghai and Shenzhen.

South Korea announces its first confirmed infection.

Human-to-human transmission is "affirmative", a Chinese expert on infectious diseases Zhong Nanshan tells state broadcaster CCTV.

Asian countries introduce mandatory screenings at airports of arrivals from high-risk areas of China.

The United States announces the first infection on American soil on January 21.

Wuhan quarantined

On January 22, the death toll in China jumps to 17 with more than 550 infections. Many European airports step up checks on flights from Wuhan.

The city is placed under effective quarantine on January 23 as air and rail departures are suspended.

The same measures are announced for two more cities in Hubei province, Xiantao and Chibi. Cases are confirmed in Singapore and Vietnam.

Beijing cancels events for the Lunar New Year starting January 25, while officials report the first death outside of Hubei.

The WHO says later on January 23 the outbreak does not yet constitute a global emergency and there is "no evidence" at the moment of the virus spreading between humans outside of China.

Cities, venues shut

By January 24, the death toll in China stands at 26, with the government reporting more than 830 infections.