A strain of bird flu has been found in chickens in Karachi, Sindh province, according to Pakistani officials.

The influenza has been identified as H-7 and H-9, strains that are said to be less dangerous than H-5N1, which is afflicting Southeast Asia.

A government circular sent to poultry farms read: "There is no solution to get rid of the said disease problem other than its eradication through destroying all birds."

As well as Pakistan, the bird flu has hit Japan, South Korea, Vietnam, Thailand, Cambodia and Indonesia. A different strain has been detected in Taiwan, while Laos has reported suspected cases in poultry.

The H-5N1 bird flu has so far killed seven people, the latest being a six-year-old Thai boy; the others were from Vietnam.

There is no evidence that the flu can be transmitted from humans to humans, but the World Health Organisation warns the outbreak could mutate and become more dangerous.