But secrecy over the contents of the agreement has concerned New Zealand, which must be consulted on security and defense issues as a former colonial power.

New Zealand’s minister of foreign affairs, Winston Peters, has accused Brown of keeping Wellington in the dark over the China deal, despite repeatedly asking for details.

“We have concerns about the Chinese state military apparatus penetrating deeply into a country that is part of the New Zealand Realm,” said a New Zealand government official, speaking on the condition of anonymity to discuss sensitive diplomatic matters.

The Cook Islands and China have said there is no security dimension to Friday’s deal, the text of which has not been released publicly.

But the agreement is expected to touch on deep-sea mining, strategic infrastructure such as ports or wharves and maritime security, all of which have security implications for New Zealand and the Cook Islands, the New Zealand official said.

Jason Young, director of the New Zealand Contemporary China Research Center at Victoria University of Wellington, said the lack of details was “deeply uncomfortable” for New Zealand considering the Cook Islands remains part of its realm.

“A comprehensive strategic partnership can range from, ‘Let’s have regular meetings and talk about political issues’ or ‘Let’s do more trade’ … to ‘How about we have policing? How about we set up a research unit on surveillance? How about we have military-to-military cooperation?’” he said.

The Cook Islands gained partial independence from New Zealand in 1965, but it still uses the New Zealand dollar and its residents receive New Zealand citizenship and passports. In December, Brown said he wanted his country to have its own passports, but he shelved the idea last week after objections from Wellington.

Neither Brown nor the Cook Islands Foreign Ministry could be immediately reached for comment Friday. Brown said last week that his government’s engagement with New Zealand had been “consistent, respectful and open,” and suggested in a social media post on Thursday that more details would be made public “in the coming days.”

The China-Cook Islands partnership comes amid a broader push by Beijing to increase its influence in the Pacific: China has signed policing agreements with both the Solomon Islands and Kiribati, drawing concern from New Zealand, the United States and other Western allies.

Beijing has also convinced several Pacific islands — including Nauru last year, and Kiribati and the Solomons in 2019 — to switch diplomatic recognition from Taiwan to China.

Very few of China’s Belt and Road initiatives or other agreements in the Pacific have ever been released, Young said. If the China-Cook Islands partnership does see the light of day, it will be because of Peters’s public pressure campaign, he said.

One area that appears likely to be covered in the agreement is deep-sea mining.

The Cook Islands has one of the world’s big exclusive economic zones, covering nearly 800,000 square miles — roughly the size of Mexico — and it is rich with polymetallic nodules containing essential metals such as manganese, cobalt, nickel and copper, all of which are needed for technologies ranging from electric cars to advanced weapons systems.

Brown visited China’s National Deep Sea Center in Qingdao, touting in a Facebook post Thursday “new areas of collaboration” between the countries, including “expanding our marine research capabilities through partnerships” and “bringing new expertise to our ongoing efforts in deep-sea exploration and sustainable ocean management.”

While many Pacific island nations have called for a moratorium on deep-sea mining — which they see as a threat to tourism, tuna stocks and other marine wildlife — the Cook Islands has emerged as one of its biggest proponents in the Pacific.

Brown has described deep-sea mining as a way for his nation of roughly 15,000 people to move beyond a reliance on tourism, while raising funds to combat the impacts of climate change and also contributing to cleaner technologies.

In 2022, Brown’s government awarded three exploration licenses to companies to search for metals to mine, a process that involves sucking up nodules from the ocean floor and which could release vast amounts of carbon. None of the companies was Chinese.

Local environmentalists fear the comprehensive strategic partnership with China will accelerate deep-sea mining in the Cook Islands, even as they, too, remain unaware of the details.

“We have no idea what is being signed,” said Alanna Smith, director of Te Ipukarea Society, an environmental organization that has called for a global moratorium on deep-sea mining while its potential impacts on marine ecosystems are studied. “That says a lot about a lack of transparency the government has with the people.”

Brown has said mining would be done hundreds of miles from shore and only if it is environmentally safe. But Smith said the government’s environmental assessments aren’t independent, and she fears deep-sea mining could effect tuna stocks on which her nation depends.

“China are all about development and speeding things up, and it’s worrying,” she said. “How much do we really need to develop and how quickly? What does this development really look like for the Cooks?”

Donald Trump’s recent inauguration adds another dimension, said David Capie, the director of the Center for Strategic Studies at Victoria University of Wellington, as New Zealand will not want to seem like it has been weak on China.

China’s claim that the agreement has nothing to do with security should be taken with a grain of salt, he added.

“You can say there is no security dimension, there’s no defense dimension, but there’s obviously deep-sea mining with surveillance and ocean cooperation,” Capie said. “The line starts to blur in terms of potential dual-use implications.”

In September, the Cook Islands’ Ministry of Foreign Affairs referred to Chinese support for a “multiuse transport hub in the Northern Cook Islands,” Capie noted.

The agreement is a boost for Beijing at a time when tensions with the Trump administration are rising.

“Despite having reasons to expand security cooperation with Pacific island nations, in reality China still faces significant challenges in doing so,” said Zhao Minghao, a professor of international relations at Fudan University in Shanghai.

Instead, China has become “more focused in maintaining its cooperative relationships with many developing countries including the Cook Islands” after Panama’s recent withdrawal from the Belt and Road Initiative, he said.

The China-Cook Islands agreement stands in contrast to Trump’s decision to dismantle USAID, which the Biden administration saw as a key plank in challenging Chinese influence in the Pacific.