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Coronaviruses are common and 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.
The novel coronavirus is different from those that have previously been identified, state broadcaster CCTV said.
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.
Possible cases have been reported in Hong Kong and South Korea involving recent travelers to China.
The 2002-2003 SARS epidemic started in southern China and killed more than 700 people in mainland China, Hong Kong and elsewhere. The new illnesses had raised fears of a SARS recurrence.