Health authorities are concerned that a virus originating in central China could spread when hundreds of millions of Chinese travel during next week's lunar new year festival.
But residents said there were was little anxiety in the city at the epicentre.
Chinese officials are cracking down on those who spread news about the disease online.
As of Friday, two people in the city of Wuhan had died following an outbreak of pneumonia linked to a new strain of coronavirus that authorities suspect originated in a seafood market.
Wuhan's health authority on Saturday said a further four people were confirmed to have the virus, bringing the total number of known cases to almost 50.
Two cases have been reported in Thailand and one in Japan, all people who had travelled from Wuhan recently.
A report published by London's Imperial College said there could be as many as 1,723 infections in Wuhan city alone.
"It is likely that the Wuhan outbreak of a novel coronavirus has caused substantially more cases of moderate or severe respiratory illness than currently reported," said the report.
"Self-sustaining human-to-human transmission should not be ruled out."
Currently the World Health Organisation and Wuhan health authorities have not concluded that the virus can be passed from person to person.
According to official statistics released on Saturday, 763 people who came in contact with victims were identified by authorities, and 98 remain under observation.
The United States and most Asian countries have stepped up screenings of travellers from Wuhan and the WHO has warned hospitals worldwide that a wider outbreak is possible.
In 2002/03, the SARS virus which originated in China killed nearly 800 people worldwide.
More than 400 million Chinese people are expected to make 3 billion trips over the new year beginning on January 24, mostly migrant workers returning to their home towns. However, many Chinese also use the holiday to go overseas.
Australian Associated Press