Those infected range from 30 to 79 years old.
The virus has now infected 62 people in Wuhan, city authorities said, with eight in a severe condition, 19 recovered and discharged from hospital, and the rest in isolation receiving treatment.
Two people have died so far from the virus, including a 69-year-old man on Wednesday after the disease caused pulmonary tuberculosis and damaged multiple organ functions.
Authorities said they had begun "optimised" testing of pneumonia cases across the city to identify those infected, and would begin "detection work... towards suspected cases in the city" as a next step, as well as carrying out "sampling tests".
Scientists with the MRC Centre for Global Infectious Disease Analysis at Imperial College in London warned in a paper published Friday that the number of cases in the city was likely to be closer to 1,700, much higher than the number officially identified.
Authorities said Sunday that some of the cases had "no history of contact" with the seafood market believed to be the centre of the outbreak. No human-to-human transmission has been confirmed so far, but Wuhan's health commission has previously said the possibility "cannot be excluded". Three cases have also been reported overseas - two in Thailand and one in Japan.
Though China has not yet reported cases outside of Wuhan, discussion about the coronavirus spreading to other Chinese cities has swelled on social media. On Sunday evening there were more than 400 million views of the hashtag "Shanghai pneumonia" on Weibo, China's Twitter-like social media site, while "Shenzhen pneumonia" garnered at least 340 million views.
China's centre for disease control moved to quash speculation about the mysterious disease on Saturday, publishing a flyer that dismissed "five big rumours".
One of them included claims about the coronavirus spreading, which China's disease control authority dismissed by saying all cases were being treated in Wuhan.
A hospital in Guangzhou, a city in southern China, also moved to dispel rumours about suspected cases of the Wuhan pneumonia, reported state-run Global Times on Sunday.
The original post, which was published through the hospital's official Weibo account on Saturday, has since been deleted. Although there has been no official announcement of screening measures on the mainland, Wuhan deputy mayor Chen Xiexin said on state broadcaster CCTV that infrared thermometers had been installed at airports, railway stations and coach stations across the city.
Chen said passengers with fevers were being registered, given masks and taken to medical institutions. Nearly 300,000 body temperature tests had been carried out, according to CCTV.
Authorities in Hong Kong have stepped up detection measures, including rigorous temperature checkpoints for inbound travellers from the Chinese mainland. The US said from Friday it would begin screening direct flights arriving from Wuhan at San Francisco airport and New York's JFK, as well as Los Angeles, where many flights connect.
Thailand said it was already screening passengers arriving in Bangkok, Chiang Mai and Phuket, and would soon introduce similar controls in the beach resort of Krabi.
Wuhan is a city of 11 million inhabitants that serves as a major transport hub, including during the annual Lunar New Year holiday when hundreds of millions of Chinese people travel across the country to visit family.