A new type of coronavirus has been identified as a possible cause of the viral pneumonia illnesses affecting dozens of people in and around China, the country's state media have said.
According to China Central Television (CCTV), the novel coronavirus is different from those that have previously been identified.
Chinese health authorities are yet to confirm the state broadcaster's report.
Coronaviruses are spread through coughing or sneezing or by touching an infected person.
Some cause the common cold and others can lead to more severe respiratory diseases, such as SARS and MERS (Middle East respiratory syndrome).
As of Sunday, the Wuhan Municipal Health Commission said 59 people in the central Chinese city were being treated for the respiratory illness. Seven were in critical condition, while the rest were stable.
Laboratory experts have so far found the novel coronavirus in 15 of those cases, CCTV said, adding that more research must be done before a conclusion is reached.
Possible cases of the same illness have been reported in Hong Kong and South Korea involving recent travellers to China.
On Wednesday, the US Centres for Disease Control and Prevention put out a health alert advising doctors who treat patients with pneumonia-like illness to consider a possible link to the Chinese outbreak and to wear masks and take other precautions in treating patients who recently travelled to Wuhan.
The CDC also advised American travellers going to Wuhan to avoid animals and sick people and wash their hands often.
