China has told New Zealand its support for the 2016 South China Sea arbitration ruling "seriously undermines" the bilateral relationship, after Wellington joined 13 other countries in a joint statement marking the ruling's tenth anniversary.

The statement, issued to coincide with the 10th anniversary of the Philippines-China South China Sea Arbitral Tribunal Award, was signed by Australia, Canada, Estonia, Germany, Italy, Japan, Latvia, Lithuania, New Zealand, the Philippines, Romania, Slovenia, the United Kingdom and the United States. It reaffirmed that the 2016 award is "final, legally binding, and definitive" between China and the Philippines, and said there is no legal basis for China's expansive maritime claims in the South China Sea, including those grounded in historic rights RNZ.

China's ambassador to New Zealand, Wang Xiaolong, responded directly to Wellington's involvement. He said New Zealand's participation "clearly deviates from the understanding reached by our leaders and seriously undermines the foundation of healthy and stable relationship." Wang added that "no one should underestimate our resolve and capability to defend our legitimate rights and interests," and called on New Zealand to "cease immediately violating China's interests" RNZ.

China's Ministry of Foreign Affairs published its own statement on 12 July, describing the tribunal decision as the "so-called South China Sea arbitration award" — the formulation Beijing has used consistently since the ruling was handed down, rejecting both its jurisdiction and its findings China's Ministry of Foreign Affairs.

A spokesperson for Foreign Affairs Minister Winston Peters said New Zealand stood by the joint statement and had no further comment RNZ. The brevity of that response is consistent with how Peters has generally handled friction points with Beijing during this term — acknowledging the position publicly while declining to engage further in the war of words.

The European Union also issued a statement on the anniversary, saying the ruling was "final and legally binding" and must be "respected and fully implemented" RNZ. Reuters reported the joint statement under the headline "South China Sea joint statement says China's maritime claims have no basis," situating the 14-nation statement within the broader anniversary coverage Reuters.

The underlying 2016 tribunal ruling found that China's "nine-dash line" — the demarcation Beijing uses to assert historic rights over most of the South China Sea — has no legal basis under the United Nations Convention on the Law of the Sea (UNCLOS). That finding has underpinned a decade of diplomatic statements from claimant states and their partners, none of which China has accepted, and none of which has altered Beijing's operational posture in the disputed waters.

For New Zealand, the calculation here sits at the intersection of two commitments Wellington has tried to hold simultaneously: a rules-based order argument grounded in UNCLOS, which New Zealand as a small maritime state has long treated as a foundational plank of its foreign policy, and a trade relationship with China that remains New Zealand's largest single export market. Signing on to a statement alongside the Philippines, the Five Eyes partners and a clutch of European states places Wellington in step with traditional security partners rather than with an independent middle-power line — a choice previous governments have made before at the point where legal principle and commercial exposure diverge.

Ambassador Wang's language, invoking an "understanding reached by our leaders," points to prior bilateral discussions — likely at leader or ministerial level — in which China had sought some assurance New Zealand would not associate itself with statements of this kind. Whether that understanding was ever formally reciprocated by Wellington, or simply raised and left unresolved, is not addressed in the public record so far. The ambassador's framing suggests Beijing regards this as a breach of an expectation set at a senior level, not merely a difference of legal interpretation.

The practical consequences for the relationship are not yet specified. Beijing has, in past disputes with other states over South China Sea statements, ranged from rhetorical rebuke through to trade friction on specific export categories. Nothing in the ambassador's statement or the Ministry of Foreign Affairs release points to a concrete measure against New Zealand at this stage. Peters' office has given no indication it expects one, and the government's public posture — restating support for the joint statement without elaboration — reads as an attempt to close the exchange rather than extend it.