Scientists believe they may have found the cause of the mystery pneumonia that has infected almost 60 people in the Chinese city of Wuhan since December.
Preliminary tests indicated the illness may be caused by a new coronavirus, lead scientist Xu Jianguo told the official Xinhua news agency.
The World Health Organisation (WHO) had also said a coronavirus could be to blame for the outbreak.
So far, 59 cases have been reported, seven of which are considered critical.
Mr Xu, who is leading efforts to identify the cause, said they had found the "new type" of coronavirus by testing infected blood samples and throat swabs collected from 15 people.
Coronaviruses can cause different diseases, ranging from the common cold to much more severe ones such as Sars and Mers. An epidemic of the potentially deadly, flu-like Sars virus occurred in 2002-3, which killed more than 700 people around the world after originating in China.
However, Gauden Galea, the WHO representative to China, said "further investigations" were required to "determine the source, modes of transmission, extent of infection and countermeasures implemented".
Singapore's airport says it will begin temperature screening travellers from Wuhan and Hong Kong health officials say they are also implementing checks on passengers.
Authorities in Hong Kong have also stepped up the disinfection of trains and aeroplanes, AFP news agency reports.
Fears the virus could be spread were further stoked by the fact it struck just before China's peak travel season, when hundreds of millions of people are set to travel for Chinese New Year later this month.
But it is still unclear how the illness is transmitted, with health officials saying no cases of human-to-human transmission had been confirmed as yet.