There are now more than 200 cases, mostly in Wuhan, though the respiratory illness has also been detected in Beijing, Shanghai and Shenzhen.
Three people have died. Japan, Thailand and South Korea have reported cases.
The new strain of coronavirus, which causes a type of pneumonia, can pass from person to person, China confirmed.
Respiratory expert Zhong Nanshan, who heads the health commission team investigating the virus, said 14 medical workers had caught it while treating patients, state media reported.