A photo taken at a recent ceremony has been forwarded to the Herald, but Devoy said INZ was unaware of the event and to date had not received any complaints.
Cellphones and cameras are banned at the ceremonies conducted by Akarana-Rewi. A woman managed to sneak the photo forwarded to the Herald.
The woman, who spoke to the Herald on the condition of anonymity, said the ceremonies were held weekly - but on different days each week.
A Tongan national, who overstayed his visitor's visa to remain with his family in Auckland, said he went to see Akarana-Rewi after his appeal to the Immigration Minister was declined.
"After losing all my money to lawyers and immigration advisers, a friend suggested I applied for my right to stay under Maori law," said the man, who paid $150 for his certificate.
"I am grateful that Chief Tupai has approved my citizenship."
He did not want to be identified and said he wouldn't go to the police because it operated under a different jurisdiction.
The man believed the certificate would give him a "basis to fight" any deportation action.
Akarana-Rewi insists the citizenship certificates he issues are legal under Maori law, and that Maori had retained their sovereignty under the 1835 Declaration of Independence.
"This is Aotearoa, not New Zealand, and the black burnt charcoal man-made law of the courts are there only based on an assumption of parliamentary sovereignty," he said.
"I have denounced my New Zealand citizenship so I am not bound by its laws, so they can arrest me or take me to court as many times as they want and it won't do anything to change my birth right and chiefly position."
Akarana-Rewi, who says he is a member of the Confederation of Chiefs of the United Tribes of Aotearoa and also a Samoan high chief, claims he has the backing of chiefs and also the United Kingdom.
"It is my view that Immigration New Zealand and the other so-called government agencies are the ones breaking the law for failing to recognise the Declaration of Maori Independence," he said.
Akarana-Rewi, who also claims to be a Ngati Whatua elder and a Ratana Church minister, said the declaration also gave Maori the right to adopt "anyone we choose".
"These people too will have every legal right to remain in Aotearoa as hapu," he said.
Devoy reiterated that INZ was the sole agency with the lawful authority to issue visas to allow people to enter or remain in New Zealand. The Department of Internal Affairs was the sole agency that could legally grant citizenship.
The agency had no record of any interaction with these bogus certificates, and did not know how many such certificates had been sold to overstayers.
"INZ encourages people who are unlawfully in New Zealand to contact us to discuss their circumstances," Devoy said.
Devoy strongly urged anyone who had been duped into paying for these certificates to contact the police.
Police spokeswoman Rachel Purdom said police had not received any complaints but urged those affected to contact police or file a complaint.
Akarana-Rewi said he had been granting citizenship to Aotearoa for "40, 50 years" and had no plans of stopping. He denied it was for profit, and said the money he charged was koha for paperwork.
He carried the British coat of arms in his wallet, which he said was what he recognised and not the New Zealand one that portrays it as a bicultural country, with a European female figure on one side and a Māori rangatira (chief) on the other.
It is estimated there are about 11,000 overstayers in New Zealand, and 2164 were deported last year, 1437 of them voluntarily.
Tonga is New Zealand's biggest source of overstayers, followed by Samoa, China, India and the United Kingdom.
People become overstayers when they enter New Zealand on temporary entry visas such as visitor, student or work visas and remain in the country after their visas expire or their applications for extensions are declined.
