Guangzhou: Two new confirmed cases of humans infected by the H7N9 strain of bird flu was reported from China's Guangdong province Monday.
The patients, aged 42 and 52, were critical, Xinhua reported, citing the provincial health and family planning commission.
Earlier this month, authorities in Guangdong and Hong Kong ordered the culling of thousands of chickens after birds exported from Guangdong to Hong Kong tested positive for the virus.
Hong Kong raised its hospital response level to "serious" from "alert" after a 68-year-old woman, who had arrived from Shenzhen two weeks earlier, was hospitalised Dec 25 with the H7N9 strain of the brd flu virus.
The World Health Organization (WHO) said in April, 2013 that H7N9 was "unlikely" to become a pandemic and that there was no evidence of human-to-human transmission. However, in July, that year, Chinese scientists found evidence that person-to-person transmission was possible, but not easy.
WHO identified H7N9 as "...an unusually dangerous virus for humans", which "is more easily transmitted from poultry to humans than H5N1".
"Avian influenza, known informally as avian flu or bird flu, refers to influenza caused by viruses adapted to birds.
It has caused a global concern because of its possible transmission to humans and the threat of a pandemic if it mutates to a form that can be easily passed from birds to humans and then, from human to human.