France has announced three cases of a deadly new virus from China, the first in Europe.

The first two confirmed cases were announced on Friday by Agnes Buzyn, the French health minister, who said both people had travelled to China.

The government later updated the number to three.

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The minister said she expects more cases.

"We have two cases," she said. "We will probably have other cases."

One reason why France is the first European country to have confirmed cases is that it has developed a test allowing medics to rapidly diagnose infected people, Buzyn said.

One of the pair, a 48-year-old man, passed through Wuhan, the epicentre in China for the virus, before travelling to France on Wednesday, she said.

That person is hospitalised in the southwestern city of Bordeaux.

The other person is in a Paris hospital.

The minister said that that person also travelled to China but that she has little other information about the case. It was confirmed shortly before she spoke at a news conference.

Earlier, the United States reported its second case, involving a Chicago woman in her 60s who was hospitalised after returning from China.

Transportation was shut down in Wuhan, a city of 11 million, and in at least 12 other cities in central China's Hubei Province, encompassing a population bigger than that of New York, London, Paris and Moscow combined.

According to the World Health Organization, signs of infection include respiratory symptoms, fever, cough, shortness of breath and breathing difficulties.

In more severe cases, coronavirus can lead to pneumonia, severe acute respiratory syndrome, kidney failure and even death.

Reports say the incubation period of the virus remains unknown, but other sources say it could be between 10 and 14 days.