Although no human-to-human infection of the H7N9 has been detected, a leading medical expert has cautioned that could happen as the virus is mutating.

Respiratory expert Zhong Nanshan said during an interview on CCTV program One on One on Sunday that human transmission can't be ruled out.

More observation on the H7N9 influenza is needed, warned Zhong who reminded people the SARS virus had a low infection rate in the early stage of its outbreak. Hundreds died in the SARS outbreak in 2003.

So far, 60 people have been infected with H7N9 in China with 13 deaths and a report of a new case in the capital Beijing.