Coronavirus outbreak: How did the virus get its name and where has it spread?

China has put millions of people in three cities on lockdown in an effort to contain a coronavirus outbreak that has killed 17 people and infected more than 630.

Health officials fear the number of infected will rise rapidly as hundreds of millions of Chinese people travel within China and abroad during the week-long Lunar New Year holidays, which begin on Saturday.

Airports worldwide have been screening passengers arriving from China. Thailand has confirmed four cases, while the United States, Singapore, Japan, South Korea and Taiwan have reported one each.

The previously unknown virus strain is believed to have emerged late last year from illegally traded wildlife at an animal market in the central city of Wuhan.

The coronavirus family includes the common cold as well as viruses behind more serious illnesses, such as the Sars outbreak which killed around 800 people during in 2002-2003.

Here are some of the key features of coronaviruses:

They get their name from their appearance under a microscope, which reveals them to be spherical and covered with crown-like spikes.

The strain found in China has been dubbed a novel coronavirus, meaning it has not been previously identified.

Those infected with cornavirus have shown a wide range of symptoms, including fever, coughing, shortness of breath and breathing difficulties.

Severe cases have caused pneumonia, severe acute respiratory syndrome, kidney failure and death.

Coronaviruses are transmitted between animals and humans, and can evolve into strains not previously identified in humans.

Preliminary research has suggested the Wuhan coronavirus may have made the jump to humans from snakes, but Chinese government medical experts have also suggested badgers and rats as possible sources.

Like other coronaviruses, it is being transmitted from person to person via droplets when an infected person coughs or sneezes.

It can also spread via contaminated surfaces, such as door handles or railings.

Like the viruses that cause Sars and Mers, the current virus is an RNA virus — meaning it has RNA rather than DNA as its genetic material — which allows it to blend with its host’s DNA and also means it can mutate rapidly.

Testing for the virus involves the use of a real-time polymerase chain reaction (RT-PCR), which identifies the viral RNA in a sample.

These could come from a throat swab, a cough sample, or a blood sample if the patient is very ill.

There is currently no vaccine for the virus.

The World Health Organisation (WHO) will decide on Thursday whether to declare the outbreak a global health emergency, which would ratchet up the international response.

Additional reporting by agencies