Authorities in China said that the number of cases of a new virus had risen to 440 and the death toll had risen to nine on Wednesday.
Deputy Director of the National Health Commission Li Bin told reporters that all the deaths were reported in the city of Wuhan in the central Hubei province.
The coronavirus is transmitted via the respiratory tract and there "is the possibility of viral mutation and further spread of the disease", Li said at a news conference.
The commission announced measures to contain the virus as millions of people travel across the country for this week's Lunar New Year holiday, including disinfection and ventilation at airports, train stations and shopping centers.
The new death toll comes less than a day after the first case in the United States was reported. Travelers from China are being screened for the virus.
"We are still in the process of learning more about this disease," said Gao Fu, an academician of the Chinese Academy of Sciences and head of the Chinese Center for Disease Control said at the same news conference.
Is the new virus a 'super spreader'?
Li said there was so far no evidence that the new virus was a "super spreader" — meaning it infects a disproportionate number of people. However, he said that it was still a possibility that was being investigated as research continues.
"We will step up research efforts to identify the source and transmission of the disease," Li vowed.
The new coronavirus has caused alarm for its similarity to SARS (Severe Acute Respiratory Syndrome), which also started in China and killed nearly 800 people in total in 2002-2003.
The World Health Organization is set to hold an emergency meeting focusing on the new coronavirus later on Wednesday.
Will the virus spread further?
"At present, during the Lunar New Year, 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 also warned.
In addition to the case reported in the US, the Chinese Special Administrative Region of Macau also noted its first case of pneumonia caused by the virus on Wednesday. The patient was a tourist from Wuhan.
Casino staff in the gambling hub have duly been ordered to don masks.
More cases have been identified in Taiwan, the Philippines, Thailand, Japan and South Korea.
Meanwhile, Hong Kong's Cathay Pacific Airlines will allow airline staff to wear surgical masks and will not charge people who want to cancel or change flights to Wuhan.
A North Korean tour agency has banned foreign tourists to guard against the spread of the virus.