While coronaviruses often simply cause harmless illnesses such as colds, strains like SARS can cause acute respiratory disease.
Illness symptoms related to the outbreak as said to include fever, cough, and difficulty breathing.
At least three of those patients are in critical condition, said the Wuhan Municipal Health Commission.
Singapore and Hong Kong have been screening air passengers from Wuhan, and USA authorities have announced similar measures at three major airports in San Francisco, Los Angeles and NY. Wuhan officials said since 14 January they are using infrared thermometers at airports, railway stations and other passenger terminals in the city to strengthen screening.
The new coronavirus strain has caused alarm because of its connection to Severe Acute Respiratory Syndrome, or SARS, which started in southern China in late 2002 and spread to more than two dozen countries killing almost 800 people.
There is no "clear evidence of sustained human-to-human transmission", since neither the patient in Japan nor the one in Thailand had visited the seafood market, according to the World Health Organization.
Wuhan's health commission also noted several epidemiologic details, including that an analysis of data of earlier cases found that some had no history of contact with the seafood market at the center of the investigation, which also sold other animals such as poultry, bats, marmots, and wild game meat.
The authorities did not explicitly state whether this was a case of human-to-human transmission. Two cases have also been reported in Thailand and one in Japan - both involving people who travelled from Wuhan.
There is no vaccine for the new virus.
A report published by the London Imperial College's MRC Centre for Global Infectious Disease Analysis asserted there are likely "substantially more cases" of the new coronavirus than the 45 now announced by Wuhan authorities.
Shenzhen is China's fourth-largest city, with a population of about 12.5 million and is about 550 air miles from Wuhan.
China said it has increased disinfection efforts in major transportation hubs to help ensure the virus does not spread.
Scott Pauley, a CDC spokesman, told VOA the CDC anticipates a higher number of Chinese travelers to the United States for the new year and has factored this into its planning.