The nine million people remaining in Wuhan, the epicentre of the disease, are equally vulnerable to the new strain of virus passing from person to person even during incubation period lasting from one to 14 days.
The National Health Commission said the virus may mutate and spread to age groups other than the 40-60 category.
Prime Minister Li Keqiang is leading a group to tackle the disease.
The virus has killed 56 people and infected more than 2,000 in China. Most of the deaths and infections have been reported from Wuhan and other cities and towns in Hubei province.
Scores of infected people who fled Wuhan last week may lead to the rapid spread of the disease to other Chinese provinces and beyond, health officials said.
China’s special administrative regions Hong Kong and Macau have reported six and five cases respectively. Three cases have been confirmed in Taiwan and 28 cases in Asia.
Canada confirmed the first case of coronavirus after a man showed symptoms of the disease after arriving in Toronto from Wuhan via Guangzhou on a China Southern Airlines flight on Wednesday.
Health officials are searching for passengers who were seated near him on the flight.
In the US, a fifth coronavirus case was reported from Arizona. A student of the Arizona State University in Tempe was infected with the virus, local media reported.