Two new human H7N9 avian flu cases have been reported in Shenzhen City in south China's Guangdong Province, local authorities said Friday.

Both patients are male, aged 50 and 53. They were confirmed to have been infected with the virus in late December, according to the municipal disease control and prevention center.

The two are being treated in hospitals in Longgang District, and one is in critical condition. Twenty-seven people who had close contact with the patients have not tested positive for the virus as of Friday.

Local health sectors have conducted investigations, risk evaluations and disinfected possible areas of transmission to prevent the virus from spreading.

H7N9, a bird flu strain most likely to strike in winter and spring, was first reported to have infected humans in China in March 2013.