As the first six Manus Island refugees move into transitional housing ahead of resettlement, PNG Prime Minister Peter O'Neill said the majority of those still in detention were not "genuine" asylum seekers and confirmed a "substantial number" would be sent home within weeks.

Mr O'Neill told the ABC that last week's riots at the Manus Island detention centre were fuelled by many detainees' anger at drawn-out processing periods and PNG immigration officials' demands for documents they did not possess.

"Many of our officials are frustrated by a lack of documentation," Mr O'Neill said on the ABC's 7.30 program.

"It is our belief that most of the refugees are not genuine ... I think many of them are just after economic opportunities that Australia and other countries offer to them and that is why they are seeking refugee status."

He said there would be "very small numbers" of other asylum seekers who would be granted refugee status in PNG.

Under questioning from host Leigh Sales about the grounds for determining most detainees did not have legitimate claims, Mr O'Neill said immigration officials were liaising with the governments of asylum seekers' home countries such as Iraq and Iran.

"How can you trust the government of Iran to tell you truthfully if somebody is likely to face persecution when they return home?" Sales asked.

Mr O'Neill said he was "hopeful" that other governments cared about their citizens and would "try and do what is best".

Tensions boiled over on Manus Island earlier this month when as many as 600 detainees launched a hunger strike.

Almost 60 asylum seekers from Somalia, Iran and Sudan were arrested by PNG police during the unrest. The PNG government also confirmed that a number of men had swallowed razor blades, stitched their lips together and had swallowed washing powder.