The virus has now infected 62 people in Wuhan, city authorities said, with eight in a severe condition, 19 cured and discharged from hospital, and the rest remaining in isolation receiving treatment.
Two people have died so far from the virus, including a 69-year-old man who died on Wednesday, with the disease causing pulmonary tuberculosis and damage to multiple organ functions.
Authorities said they had begun "optimised" testing of pneumonia cases across the city to identify those infected with the virus, and would begin "detection work... towards suspected cases in the city" as a next step.
A paper published Friday by scientists with the MRC Centre for Global Infectious Disease Analysis at Imperial College in London warned that the number of cases in the city was likely to be closer to 1,700 than those officially identified.
Authorities said Sunday that some of the new 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.
While mainland China has not yet announced any travel restrictions, 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.
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