SYDNEY (AFP) - An outbreak of polio has been confirmed in Papua New Guinea as per WHO with the virus detected in a child, 18 years after the Pacific nation was declared free of the disease.

The WHO said there was one confirmed case - a six-year-old boy with lower limb weakness from Morobe province - with the disease detected in late April, and paralysis associated with the virus confirmed in May.

The US Centres for Disease Control and Prevention said the same virus was also isolated from stool specimens of two healthy children in the same community, "representing an outbreak".

According to the WHO, the number of polio cases worldwide has fallen by more than 99 per cent since 1988, from an estimated 350,000 cases then to 22 reported cases in 2017.

Only three countries - Afghanistan, Nigeria and Pakistan - were considered polio-endemic by the WHO in March.