Prime Minister John Key says the whistle blower who targeted him over the so-called Panama Paper leaks is probably European and confused about New Zealand and the Cook Islands sharing the same currency.

In a statement issued overnight, the whistleblower called out Key for being "curiously quiet" on "the financial fraud mecca that is the Cook Islands".

The anonymous "John Doe" is confirmed by German newspaper Suddeutsche Zeitung as the whistleblower behind the biggest data leak in history, known as the Panama Papers.

JOSHUA ROBERTS/REUTERS

The source behind the Panama Papers leak has taken aim at New Zealand Prime Minister John Key.

Speaking in Auckland on Saturday, Key said he had about as much responsibility for Cook Island tax affairs "as I do for taxing Russia".

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CARLOS JASSO/REUTERS

More than 11.5 million financial and legal records from Mossack Fonseca were leaked.

"That's why I'm quiet on it - because I don't have responsibility for it."

Key said New Zealand had responsibility for Cook Island defence and foreign affairs matters, but not tax.

He said the data leak appeared to be referring to matters dating back to before 1988, before tax loopholes were closed.

"Prior to 1988 there were issues about New Zealanders avoiding their tax by having a structure in the Cook Isands….that well and truly predates me.

"The whistle blower has got confused about my responsibilities. I have no responsibility for the tax jurisdiction of the Cook Islands. New Zealand has responsibility for foreign policy and defence of the Cook Islands but not for tax.  I  have as much responsibility for tax in the Cook Islands as I do for taxing Russia."

Key said he had asked a tax official why someone might link him to the Cooks "and they said he or she is likely to be European. The Europeans get terribly confused about the Cook Islands because they use New Zealand dollars."

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In a statement issued to the German newspaper Süddeutsche Zeitung and the International Consortium of Investigative Journalists, the so-called "John Doe" behind the leak calls for better whistleblower protection and hints at even more revelations to come.

In the 1800-word statement, titled "The Revolution Will Be Digitized", the source behind the leak says "income inequality is one of the defining issues of our time", and that government authorities need to do more to address it.

"Prime Minister John Key of New Zealand has been curiously quiet about his country's role in enabling the financial fraud Mecca that is the Cook Islands," the statement says.

Key said he was aware he had been singled out over the Cook Islands in the overnight statement, but said it was historic.

Meanwhile, Key said he was confident neither he nor any of his ministers would be on a list of several hundred names due to be released on Monday morning.

"I won't be on that list. These people have had these papers for a year looking through politicians," he said.

"I know my own personal situation. I can assure you if I'd been in it or my ministers had been in it, we'd well and truly know by now. He's made reference to me as the Prime Minister of New Zealand.

"We haven't seen the papers so we can't comment in any great note and when we get the chance we'll work our way through them."

The whistleblower said they would consider releasing papers to government under certain conditions, something Key said he would consider.

"If there are new things that come out, we want to secure our tax base and we want to make sure our reputation on being up front on all these matters is preserved, that's been the view of the OECD and if there's something to tell them, if not we'll take measures to resolve it," he said.

The so-called Panama Papers - more than 11 million documents in total - detail the financial affairs of clients of Panamanian law firm Mossack Fonseca, lifting the lid on a world of secret trusts and tax havens.

The papers also show how Key's lawyer, Ken Whitney, furnished the Panamanian law firm Mossack Fonseca with a professional reference for an Auckland law firm.

The Australian Financial Review has revealed New Zealand's role as a player in that world, because of our trust laws.

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