China is warning that the mysterious Wuhan coronavirus is mutating, meaning it could spread further and become harder to control.

Chinese authorities have confirmed 440 cases of infection and blamed the virus for nine deaths, while cases have been reported in other countries as well.

China's National Health Commission said 2,200 people had identified as having been in close contact with people who had the virus and that 1,400 were under observation.

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Chinese authorities are warning that the mysterious virus blamed for at least nine deaths is appearing to "mutate" and could spread further, with transmission possible from person to person.

Li Bin, the deputy director of China's National Health Commission, told reporters on Wednesday that 2,197 people had identified as having been in close contact with people who had the virus.

He said 765 of those people had been released from medical observation but that 1,394 were still being observed.

Gao Fu, the director-general of China's Center for Disease Control and Prevention, also said on Wednesday that the virus was adapting and mutating — making it harder to manage and control.

It is common for viruses to mutate, but doing so makes them more dangerous as they might become immune to treatments designed to tackle them. The flu is an example of a virus that mutates; the mutation is why different flu vaccines are needed each year.

Li Bin, right, of China's National Health Commission, answering questions from reporters about the Wuhan virus in Beijing on Wednesday. NOEL CELIS/AFP via Getty Images

"We are still in the process of learning more about this disease," he said.

Li said that officials believed the virus was mainly spread "through the respiratory tract" and that "there is possibility of viral mutation and further spread of the disease."

China had confirmed 440 cases of infection in the country as of midnight on Tuesday — a figure that increased ninefold in just one week.

The virus, called 2019-nCoV, is a coronavirus — which is one that infects the nose, throat, or sinuses — and causes pneumonia-like symptoms.

Li on Wednesday attributed the growing number of confirmed cases at least in part to greater monitoring efforts and understanding of the virus.

Authorities had confirmed earlier this week that the virus, which has been linked to a market selling animals, could be spread among humans, despite an earlier belief that humans were able to catch it only from animals.

Some cases of the virus have spread from the central Chinese city of Wuhan to other parts of China, and cases have also been confirmed in the US, Taiwan, Japan, Thailand, and South Korea.

Other countries have reported suspected cases of the virus.

Travelers being screened with infrared thermometers at Hankou Railway Station in Wuhan on Tuesday. Associated Press

The World Health Organization is holding an emergency meeting on Wednesday to determine whether to declare the outbreak a global health emergency.

And fears of a spread has been heightened as hundreds of millions of people prepare to travel throughout China and beyond to mark the major Lunar New Year holiday.

"The rise in the mobility of the public has objectively increased the risk of the epidemic spreading and the difficulty of prevention and control," Li said Wednesday.