New Zealand snoops on the phone calls, emails, Internet browsing sessions and online chats of government ministers and senior officials in Pacific island nations, including French territories in the region, the New Zealand Herald reported.
Western interest in the South Pacific has risen in recent years as China increases aid and diplomatic activities in a region that New Zealand and Australia traditionally regard as their sphere of influence.
The newspaper said documents supplied by US whistleblower Edward Snowden showed the extent of New Zealand's spying on behalf of the "Five Eyes" intelligence network, which also includes the United States, Britain, Australia and Canada.
Separately, the Sydney Morning Herald said the documents also revealed New Zealand and Australian intelligence services worked together to spy on Indonesia's largest mobile phone network Telkomsel.
More From This Section
The Intercept said New Zealand's Government Communications Security Bureau (GCSB) used its Waihopai base in the country's South Island to collect vast amounts of data from the region, most of it from friendly nations.
Nations reportedly subjected to New Zealand's wholesale snooping included Fiji, Samoa, Tonga, the Solomons Islands, the Cook Islands, Kiribati, Vanuatu, Nauru and France's overseas territories New Caledonia and French Polynesia.
Tongan Prime Minister 'Akilisi Pohiva reportedly told Fairfax Media that such a programme would be a "breach of trust" but added "it is happening all over the world".
"Tonga is too small to stand up to the alleged spying. China is on the radar... So what can we do?" he said.
"It's gone on for a very long period of time but there are good reasons why," he told commercial radio.