Photo: Supplied / World Health Organisation

The number of children confirmed to have polio in Papua New Guinea has increased to 21 according to the World Health Organisation.

Cases have been found in nine provinces - nearly half the country - since the outbreak was first discovered in Morobe in June.

One child has died.

Meanwhile, the WHO said a nationwide vaccination campaign has covered 92 percent of the country.

It said more than 3 million children have received their first round of vaccines.

It's pleading with parents to ensure their children receive their second and third doses.