Hundreds of protesters have marched on Cook Islands’ parliament to oppose prime minister Mark Brown’s recent decisions, including a failure to properly consult its closest partner New Zealand over a deal to deepen ties with China.

Roughly 400 protesters – led by opposition parties – gathered outside the capital city of Avarua on Tuesday, RNZ reported, with some holding signs reading “Stay connected with New Zealand”. Others waved placards showing the New Zealand passport in opposition to Brown’s now-abandoned controversial proposal to introduce a separate Cook Islands passport, which New Zealand warned would require holders to renounce their New Zealand one.

“We have no problem with our government going and seeking assistance,” opposition leader Tina Browne said. “We do have a problem when it is risking our sovereignty, risking our relationship with New Zealand.”

Last week, the prime minister signed an “action plan for the comprehensive strategic partnership” with Chinese premier Li Qiang in the northern city of Harbin during a five-day state visit to China. Brown said the accord set a framework for engagement in areas including trade, investment, ocean science, infrastructure and transport.

After returning home on Monday from China, Brown told reporters he would release the full details of the agreement soon, and said China will provide the Pacific nation of 17,000 people with a one-time grant of about $4m.

“Our ministries will be looking carefully at where they would look to allocate that funding as part of projects or initiatives that we might want to promote. And at this stage, it’s looking like primarily in the area of renewable energies,” Brown told Cook Islands News.

The self-governing Cook Islands has a “free association” relationship with New Zealand, which provides budgetary assistance as well as helping on foreign affairs and defence. Its citizens hold New Zealand citizenship.

New Zealand expressed “significant concern” about a lack of transparency over the trip, amid growing concerns over China’s push for influence in the region, and alarm that Brown failed to properly consult New Zealand officials over the deal, which is an obligation within the special constitutional arrangement between the two nations.

Brown said Wellington should not have any concerns after it reviews the deal. The details will be “out online very shortly, people can see for themselves,” he told reporters.

China and Cook Islands last week signed several bilateral cooperation documents over economy, environment, culture and other sectors, in Harbin, China’s foreign ministry said on Monday.

Cook Islands officials say they also discussed seabed minerals research with Chinese institutes during the visit, as the Pacific island mulls deep-sea mining of nodules rich in metals such as nickel and cobalt.

China is vying for diplomatic, economic and military influence in the strategically important Pacific, challenging the influence of Australia, New Zealand and the United States in the region.

China’s state news agency Xinhua earlier quoted Li as saying the agreement would “deepen political mutual trust and expand practical cooperation with the Cook Islands”.