A major undersea telecommunications cable that connects Australia and New Zealand to North America has been tapped to allow the United States National Security Agency and its espionage partners to comprehensively harvest Australian and New Zealand internet data.

Documents published by The Intercept website by former US intelligence contractor Edward Snowden show that New Zealand's electronic spy agency, the Government Communications Security Bureau (GCSB), worked in 2012 and 2013 to implement a mass metadata surveillance system based on covert access to the Southern Cross undersea cable network.

New Zealand Prime Minister John Key denied there had been mass surveillance. Credit:Getty

Founded in 1997, Southern Cross owns and operates a Trans-Pacific submarine cable network connecting Australia, New Zealand, Fiji and Hawaii to the internet backbone on the west coast of the United States. The network was developed to service the rapid growth of Internet traffic across the Pacific. It is owned by Telecom New Zealand with a 50 per cent share, SingTel Optus (Australia's second-largest telecommunications provider) with 40 per cent and Verizon Business with 10 per cent.

Top secret documents provided by Mr Snowden show that the GCSB, with ongoing cooperation from the US National Security Agency, implemented Phase I of a mass surveillance program code-named "Speargun" at some time in 2012 or early 2013.