China's state news agency's warning to John Key

AUCKLAND, NEW ZEALAND - JANUARY 27: New Zealand Prime Minister John Key delivers his state of the nation speech to the Auckand Chamber of Commerce at the Langham Hotel on January 27, 2016 in Auckland

China's state news agency Xinhua has warned Prime Minister John Key to steer clear of talking about territorial disputes in the South China Sea if he wants any traction in trade talks.

Mr Key left for China today for a visit focusing on talks to "upgrade" the New Zealand China free trade agreement.

Mr Key will meet China's President Xi Jinping on Tuesday. While trade is expected to be the main topic, Mr Key has also said he will raise the South China Sea issue.

However, an editorial in Xinhua, often the Chinese Government's mouthpiece, has warned future relations could be endangered by recent comments about the South China Sea -- comments it said were critical of China despite New Zealand's claim not to take sides in the dispute. It said New Zealand should take its own stance rather than be "hijacked by the ambitions of its military allies".

"Key should be reminded that New Zealand is an absolute outsider in the dispute and not a concerned party, and that any attempt by Wellington to break its promise not to take sides on the issue would risk complicating the flourishing trade ties between China and New Zealand."

Xinhua also said it was baffling that New Zealand was taking part in a military exercise in the South China Sea during Mr Key's visit. That exercise -- Bersama Shield -- will be hosted by Malaysia, which is one of many countries in dispute with China over territory in the South China Sea. It simulates a situation in which Malaysia and Singapore are under threat by an unnamed force. Defence Minister Gerry Brownlee has denied it is provocative and while it is in the South China Sea it is not in a part China has a dispute over. The New Zealand Government has consistently refused to take sides in the South China Sea argument but this year both Mr Key and Foreign Minister Murray McCully have increased criticism of ongoing reclamations and military buildups in the disputed territory. Both were careful not to directly name China, instead urging caution by all countries involved, but China was seen as the primary target of the concern.

The talks to upgrade the trade agreement follows China's trade agreement with Australia which got some more favourable terms than New Zealand. The terms of the agreement allow for changes when either country negotiates a more favourable trade agreement with another country. New Zealand's entry into the Trans Pacific Partnership is also likely to require re-negotiating of the China agreement in some areas.