Anyone who concealed new cases would "be nailed on the pillar of shame for eternity", the political body responsible for law and order said.
The warning came as state media said six people had now died from the virus, which causes a type of pneumonia.
It's been confirmed the virus can pass from person to person.
The World Health Organization (WHO) will on Wednesday consider declaring an international public health emergency over the virus - as it did with swine flu and Ebola. Such a declaration, if made, will be seen as an urgent call for a co-ordinated international response.
China's National Health Commission on Monday confirmed for the first time that the infection could be transmitted from human-to-human. It said two people in Guangdong province had been infected in this way.
In a separate statement, the Wuhan Municipal Health Commission said at least 15 medical workers in Wuhan have also been infected with the virus, with one in a critical condition.
The workers presumably became infected with the virus due to contact with patients. All of them are being kept in isolation while being treated.