New Zealand raised concerns that the People's Liberation Army (PLA) was outspending it on aid to defence forces in the region, particularly Fiji, Tonga and Papua New Guinea, the cables released by the WikiLeaks website said.
In a 2008 cable, US diplomats noted New Zealand was worried Pacific nations "are increasingly turning away from Australia and New Zealand to seek ties with Taiwan, China, Cuba and others", the Dominion Post newspaper reported.
Another briefing from 2006 quoted defence ministry deputy secretary Chris Seed as saying "PLA activities in the Pacific Islands pose real security problems for New Zealand", the NZ Herald newspaper reported.
New Zealand, along with Australia, has traditionally seen the South Pacific as its sphere of influence but the cables show disquiet at China's activities as Beijing vied with Taiwan for diplomatic influence in the region.
One US cable, dated September 2006, said New Zealand's foreign affairs department complained that China spoke about responsible development in the region but "practises the opposite when it comes... to competing with Taiwan".
China's "rapacious quest" for natural resources undermined good governance and sustainable development in Pacific nations, another cable from the same year quotes the foreign affairs department as saying.
Other cables released by WikiLeaks earlier this month showed the US and New Zealand last year ended a near 25-year break in intelligence collaboration sparked by Wellington's anti-nuclear stance but kept the news secret.
The New Zealand government has a policy of not commenting on WikiLeaks releases.
Relations between Wellington and Beijing have warmed in recent years, with New Zealand signing a free trade agreement with China in 2008.
China is New Zealand's second largest trading partner after Australia, according to official data.