A spokeswoman for Prime Minister John Key refused to comment last night. "It's been the longstanding practice of New Zealand governments not to comment on foreign intelligence matters," she said.
Greenwald has drawn comparisons between the value of New Zealand's image as a harmless, friendly nation with spying revelations that sundered Canada's relations with Brazil and raised questions over diplomatic missions to other countries.
The Canadian equivalent to the GCSB targeted Brazil with hacking tools to access computers and devices belonging to other countries. Documents showed Canada's eavesdropping agency used the nation's benign reputation to set up covert spying sites in 20 "high-priority countries".
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Greenwald said part of New Zealand's value to the Five Eyes was "its relationship with other countries the US might not have access to".
He said the Canadian example showed "how the NSA [National Security Agency] uses Canada to access certain places on the planet which for whatever reason the NSA cannot access, and they gather data for the NSA".
"Absolutely New Zealand does exactly the same thing and the language in the documents that are used to describe the NSA-GCSB relationship are almost identical," he said.
On that list of countries that the GCSB spies on are adversarial countries that probably New Zealand would expect to be on that list but also [other] democracies and allied countries that I think a lot of New Zealanders would be surprised about."
Asked about whether New Zealand was spying in China, he made it clear he had not specifically singled out the country but said it was dealt with in an upcoming story.
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"I said that is part of the reporting I am doing, especially given the consequences of that revelation.
"I think there is probably an expectation that China has that there is some surveillance going on. China knows full well New Zealand is part of the Five Eyes alliance and they know how that functions.
"The extent of it, the purposes of it, would - I would think - create a lot of discomfort diplomatically."
He said the issue became huge in Canada over the Brazilian spying because it was done for economic reasons. "Canadians just don't think of themselves as the kind of country that spies on the agencies of other countries for purely economic ends. I think there's a bit of that going on in New Zealand too."
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Greenwald said documents from the Snowden archive showed New Zealand benefited from the information gathered by the Five Eyes.
The grouping of nations was also driven by a unifying purpose: "'Collect it all' is the motto. It appears over and over again in those documents.
"Mass surveillance is the principal goal and purpose of the Five Eyes alliance."
The Chinese Embassy was asked for comment but did not respond.
Cheryl Gwyn, the Inspector-General of Intelligence and Security, said she had not identified "any indiscriminate interception of New Zealanders' data".
"As part of my role as Inspector-General, I review whether the GCSB complies with the restrictions upon interception of New Zealanders' communications and with the requirement to intercept communications only for authorised purposes. That review is ongoing.
"I am only able to comment on specific GCSB activities through my annual and inquiry reports. However, I can advise that I have not identified any indiscriminate interception of New Zealanders' data in my work to date. I will continue to monitor these issues."
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