GUANGZHOU - South China's Guangdong province reported another human case of the H7N9 strain of avian flu, local authorities said on Thursday.

The 58-year-old man surnamed Lin is in a critical condition in a hospital in Shenzhen city, the provincial health and family planning commission said in a statement.

The health authorities warned that people are most at risk at catching bird flu during winter and spring.

In addition to Guangdong, Shanghai municipality and Fujian and Zhejiang provinces have all reported human cases of H7N9 this winter.