New Zealand's role in the Five Eyes surveillance alliance has been a sideshow to debates that have erupted in the US, the UK, and Europe since former NSA contractor Edward Snowden began releasing his trove of classified documents.

But that may change tomorrow night, NZ time, at the Auckland Town Hall.

With five days left until a general election, Kim Dotcom, founder of the Internet Party contesting that election, is being joined by Glenn Greenwald, who is promising to reveal information showing that New Zealanders have been the subject of mass surveillance by their own government.

If he delivers, that will draw statements made by New Zealand Prime Minister John Key into question. The prime minister has already promised to resign if mass surveillance has taken place.

Key, who called Greenwald "Dotcom's little henchman", said he will declassify documents to prove he has been telling the truth. He said New Zealand's communications security agency GCSB looked into a plan for such mass surveillance after a series of cyber attacks, but that the plan was rejected and never implemented.

The election has already been disrupted by the hacking of a controversial blogger's emails that led to the resignation of a government minister.

Edward Snowden is expected to beam in from exile in Russia, presumably on the same subject: New Zealand's role in the Five Eyes alliance.

Dotcom, meanwhile, is promising to show that he was granted citizenship to trap him in New Zealand and facilitate his eventual extradition to the US. Dotcom faces racketeering charges there related to his now forcibly shuttered file-sharing website Megaupload.

Now add Julian Assange into the mix. Exactly what Assange will contribute is not yet known, but he is scheduled to beam in from his sanctuary, the Ecuadorian embassy in London.

Greenwald arrived in New Zealand two days ago to immediately embark on a series of media interviews previewing his upcoming revelations, which he says will be published on his website The Intercept to coincide with the Auckland event.

Greenwald said he has been working on the New Zealand part of the Snowden reporting for several months. The New Zealand government, he said, made statements in connection with a new spying law that was enacted last year, including assuring that it did not engage in mass surveillance and doesn't target New Zealanders indiscriminately.

"One of the things that we wanted to do was to investigate the truth of those statements and to do the reporting that would let New Zealand citizens know whether or not their government deceived them about what these spy agencies are doing, and I can tell you — although I can't tell you what the reporting is yet — I can tell you that there are serious questions about whether the current government was at all truthful with its citizens in connection with that Bill," he said.

Greenwald said there are no "bit players" in the alliance.

"Obviously, some countries are bigger and spend more money on surveillance than other countries within the alliance, and New Zealand is on the end of the countries that spend fewer rather than more resources, but New Zealand spends an extraordinary amount of resources, for a country of this size, on electronic surveillance, and every single thing that the NSA does that we have been reporting on over the last year and a couple of months involves New Zealand directly.

"They are full-fledged allies of this effort."

Greenwald added that New Zealand is also helping the US to spy on other nations in the region.