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Snowden, who is sheltering in Moscow from US attempts to extradite him on espionage charges, appeared by video link before a capacity crowd at the Kim Dotcom organised Moment of Truth event at Auckland Town Hall this evening.
"There are actually NSA facilities in New Zealand that the GCSB [Government Communications Security Bureau] is aware of and that means the Prime Minister is aware and one of them is in Auckland another is in the north of the country," Snowden said.
The event took place shortly after Snowden claimed in an online article to have evidence of mass surveillance of New Zealanders' electronic communications by New Zealand's GCSB.
That article was published by visiting US journalist Glenn Greenwald, who has made the same claims and who introduced Snowden to the audience of about 1700.
Snowden, Greenwald said, was "overwhelmingly considered a hero" overseas for his work exposing the NSA's spying.
"Even his harshest critics have not been able to say anything he has said about surveillance is unreliable or untrue."
Snowden began his talk with the claim the NSA had a facility in Auckland and went on to expand on his article in which he said: "If you live in New Zealand, you are being watched."
In his work as an NSA analyst, he claimed he routinely came across the communications of New Zealanders.
That information was available to NSA analysts through a surveillance tool called X-Keyscore.
Information about New Zealand communications was available simply by clicking on a check box in that software.
This evening, to huge cheers, he told the audience that if political leaders were "going to use check boxes against us ... election time is when we get to check boxes about them".
When asked by reporters afterwards why he didn't talk about proof Mr Key knew of him before the raid on his mansion, Dotcom said: "I think the evidence is pretty clear today in the Herald".
"It's going through the official process in Parliament, we're going to give the Prime Minister the due process that he denied me."
Dotcom said he believed the email was "100 per cent true".
In an at times heated press conference, Dotcom responded to question about the email by saying the evening was about the issue of mass surveillance.
Dotcom became angry at reporters' questions, saying the media should have better held the Government to account.
"You have not done that, you have failed New Zealanders in the past. You need to wake up and do your jobs."
Dotcom said he had "focussed on the much bigger lie" around mass surveillance rather than his personal issues with Mr Key.
"That is the story, get your priorities right," he angrily told reporters.
Questioned about his motivations about the timing of his reports and visits, Greenwald told reporters: "The suggestion we have some sort of interest in shaping the outcome of your election ... is absurd.
"What I know about is the surveillance activity of the New Zealand Government and that's what I'm here to talk about."
By Adam Bennett of the New Zealand Herald