China's People's Liberation Army (PLA) dates its origins to 1 August 1927, when Communist troops rose against Chiang Kai-shek's Nationalists in the city of Nanchang. The uprising failed, but the Communists went on to win the civil war on the mainland, a war that never formally ended. In 1949, Chiang's government retreated to Taiwan, taking the Republic of China with it.

Next August, the PLA turns one hundred. For New Zealand, which sends a quarter of its goods exports to China, how Beijing marks the anniversary is no distant affair.

For Xi Jinping, Taiwan remains unfinished business. He pledges to 'strive for peaceful reunification', but says China will 'never promise to renounce the use of force'. The Pentagon judges that China expects to be able to win a war over Taiwan by the end of 2027. US intelligence says no invasion is currently planned for next year.

In the meantime, Taiwan is preparing for a quarantine of its ports by China's coast guard. New Zealand should do the same.

In 2025, China bought US$11.6 billion of New Zealand's goods, 24.8 percent of its goods exports. In some sectors the exposure is particularly sharp. China takes 62 percent of New Zealand's wood and 55 percent of its infant formula.

A quarantine, let alone a blockade, would not stop there. It would also disrupt trade with Japan, South Korea and Taiwan itself, putting 37 percent of New Zealand's goods exports at risk.

For decades, Wellington has walked a careful line, trading with Beijing while relying on Canberra for its defence. A quarantine is designed to make that line impossible to hold, even without declaring war.

Should a New Zealand exporter let a Chinese coast-guard officer inspect its cargo? Should the operation be called a blockade, as New Zealand's allies might, or law enforcement, as Beijing would? And what would New Zealand offer if its ally Australia asked for help? Every answer would require a stand to be taken.

Ministers should settle now, confidentially and with the opposition, how New Zealand would describe a Chinese quarantine, what it would advise exporters asked to submit to inspection and how it would respond to a request from Canberra. A Taiwan crisis should be treated as a national one from the outset, especially if it coincided with renewed disruption in the Gulf, with a coordinator named in advance and each agency leading in its own field.

However Beijing chooses to mark its army's hundredth year, New Zealand will need a reply that is thought through in advance if it is not to fall off the tightrope.