An expert with the country's agricultural ministry has said that migratory birds may have carried the H7N9 avian influenza virus into China.
According to health authorities, a total of 20 H7N9 cases have been reported in the country till Sunday evening, including the six cases that ended in fatalities.
As the source of infection and its transmission remained unclear, the possibility of migratory birds carrying the H7N9 avian influenza virus into the country could not be ruled out, Xinhua quoted Yu Kangzhen, the chief veterinarian with the agriculture ministry, as saying Sunday.
The virus has mostly been found in live poultry trading markets, not in farms raising poultry, he said, adding the virus had not been found in pigs so far.
He said the number of most infections have been reported from Shanghai, but the possibility of the virus spreading further also existed.