Malawi's health authorities have declared a polio outbreak after a case was detected in a young child in the capital Lilongwe, the World Health Organization said on Friday.

This is the first case of wild poliovirus in Africa in more than five years, the WHO said in a statement.

Laboratory analysis showed the strain detected in Malawi was linked to one that has been circulating in Pakistan, where it is still endemic.

"As an imported case from Pakistan, this detection does not affect the African region's wild poliovirus-free certification status," the WHO said, adding it was taking urgent measures to prevent polio spreading.

"Thanks to a high level of polio surveillance in the continent and the capacity to quickly detect the virus, we can swiftly launch a rapid response and protect children from the debilitating impact of this disease," said the WHO's regional director for Africa, Matshidiso Moeti.