WELLINGTON - China on Sunday expressed concern about a report that New Zealand and United States spy agencies planned to hack into a data link between Chinese government buildings in Auckland.

The plan was revealed in documents from US National Security Agency (NSA) whistleblower Edward Snowden, the Herald on Sunday newspaper reported.

The project run by New Zealand's Government Communications Security Bureau (GCSB) and the NSA appeared aimed at tapping data flowing between the Chinese Consulate and its visa office in Auckland.

The documents said the GCSB had identified the data link, and agreed to cooperate with the NSA to use the link to access China's computer systems, said the report.

Documents appeared to show the plan was codenamed "Frostbite" by the GCSB and "Basilhayden" -- also identified as fictional spy James Bond's drink of choice -- by the NSA.

The paperwork revealed the GCSB worked with the NSA's elite hacker team -- the Tailored Access Operations division -- which specialized in cracking computer systems and planting spyware on computers, said the report.

A 2013 NSA document showed China at the top of a list of targets it was having monitored by the GCSB, saying the New Zealand agency gave the NSA "access to areas and countries that are difficult for the United States to access."

But it is unknown if the plan went ahead because, as sign-off was being sought, Snowden walked out of his job with a mass of top secret documents.

The Chinese Embassy in New Zealand issued a statement Sunday, saying that China was concerned about the report and attached great importance to the cyber security issue.

"We will firmly safeguard our security interests and continue to guarantee our cyber and information security with concrete measures," said the statement.

"At present, cyber space is riddled with chaos and uncertainty. China proposes to settle disputes through dialogue and formulate codes to regulate cyber space behaviors that are acceptable to all sides."

Xinhua was unable to contact anyone in New Zealand Prime Minister John Key's office for a response on Sunday, but the Herald on Sunday reported that a spokeswoman for Key said the government would not respond to claims made from documents "stolen " by Snowden.

She said the intelligence agencies contributed to "our national security and the security of New Zealanders at home and abroad."

The opposition Green Party said Key and the government pointlessly endangered New Zealand's relationship with its largest trading partner.

"Breaking international agreements to spy on Chinese diplomatic communications in Auckland is reckless. It would bring very little, if any, benefit to New Zealand," Greens co-leader Russel Norman said in a statement.

"The test is, would we have spied on China on our own accord? It's very unlikely. So why is New Zealand spying on behalf of the Americans?"