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

The statement 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 Philippines-China South China Sea Arbitral Tribunal Award is "final, legally binding, and definitive" between China and the Philippines, and said there is no legal basis under international maritime law for China's expansive claims in the South China Sea, including those it grounds in historic rights.

China's ambassador to New Zealand, Wang Xiaolong, responded directly. 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, referring to the tribunal decision as the "so-called South China Sea arbitration award" — a consistent formulation Beijing has used since the ruling was handed down, rejecting both the tribunal's authority to decide the case 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. That brevity reflects how Peters has handled other points of friction with Beijing during this term — publicly restating New Zealand's position while declining to extend the disagreement.

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 14-nation statement, framing it as addressing the absence of any legal basis for China's maritime claims 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 standing under the United Nations Convention on the Law of the Sea (UNCLOS), the treaty that sets out nations' maritime rights and limits. That finding has supported a decade of diplomatic statements from countries with competing claims and their allies, none of which China has accepted, and none of which has changed Beijing's military and civilian activities in the disputed waters.

For New Zealand, this decision sits at the intersection of two commitments. The first is support for a rules-based international order anchored in UNCLOS, which New Zealand as a small maritime nation has long treated as central to its foreign policy. The second is its trade relationship with China, which remains New Zealand's largest single export market. Signing on alongside the Philippines, the Five Eyes partners, and European states places Wellington with its traditional security allies rather than on an independent middle-power line — a choice earlier governments have also faced when legal principle and commercial interests pull in different directions.

Ambassador Wang's reference to an "understanding reached by our leaders" suggests prior bilateral discussions at leader or ministerial level, in which China had sought assurance that New Zealand would not sign statements of this kind. It is unclear from the public record whether that understanding was ever formally confirmed by Wellington, or simply raised and left unresolved. Wang's language suggests Beijing views this as a breach of an expectation set at senior level, not merely a difference in how the law should be read.

The practical consequences for the relationship remain unspecified. In past disputes with other countries over South China Sea statements, Beijing has responded with everything from rhetorical criticism to trade friction on specific exports. Nothing in Wang's statement or the Ministry of Foreign Affairs release points to concrete measures against New Zealand at present. Peters' office has given no sign it expects such action, and the government's public approach — restating support for the joint statement without elaboration — reads as an attempt to contain the dispute rather than extend it.