Guangxi has reported a boy contracted the H7N9 strain of bird flu, a day after his mother was confirmed to have the virus.
The Guangxi health bureau said the boy, aged five and from Heng county in Nanning , started coughing and had a fever on Monday and was diagnosed with the disease yesterday.
Health authorities are still determining how the boy became infected, but said he had been in close contact with his mother, 41.
She began to feel unwell late last month while in Zhongshan in Guangdong, and returned to Nanning on January 28.
The boy was stable but his mother's condition was critical.
Xinhua reported that the national health commission said yesterday there was no proof the H7N9 was spreading sustainably from person to person.
The National Health and Family Planning Commission said earlier it could not rule out "limited" human-to-human infections of H7N9.
Last month, Zhejiang province reported that a man, his wife and daughter in Xiaoshan district, Hangzhou , had contracted the virus. The 49-year-old father died. But experts were not certain if human-to-human transmission was involved because all three had been exposed to poultry in wet markets.
Meanwhile, nine other cases were reported yesterday - four in Guangdong and Zhejiang respectively, and one in Fujian , Xinhua reported. The new cases in Guangdong included a girl, 5, and a man, 42, in Zhaoqing; a man, 49, in Foshan and a man, 56, in Shenzhen.