Sydney: Papua New Guinea has reportedly told the Australian government it will not be allowed to walk away from the asylum-seekers currently held in the Manus Island Detention Centre in October.

The country's newly-appointed Attorney-General Davis Steven told the ABC his government had not agreed to close the camps by the end of October.

That contradicts an agreement between the nations announced by Immigration Minister Peter Dutton in July.

"I am the chief legal advisor to government. I have not sighted a formal document that confirms that date has been mutually agreed," Mr Steven said on Friday.