The World Health Organisation has said the outbreak in Asia of the contagious bird flu virus poses a significant risk and could not be adequately dealt with by countries operating on their own.

The WHO said it remained concerned that bird flu could mutate or combine with another virus to cause a world pandemic.

Up to two million chickens have died in Pakistan following an outbreak of the virus there, but no humans have so far been affected. Officials say a strain of bird flu has been found in chickens in the southern port of Karachi.

Officials in Thailand, who earlier reported the death of a six-year-old boy from bird flu, now say there may have been up to five more fatalities

So far, seven people have been confirmed dead in Asia from the disease which is contracted by exposure to infected poultry. The other victims, most of them children, died in Vietnam.

The head of the department for disease control in Thailand has said a second youth remains ill in hospital after testing positive for the virus.

Cases of the flu have also been confirmed in Cambodia, Japan, South Korea and Indonesia.