Cook Islands Prime Minister Mark Brown will make a state visit next week to Beijing, where he is expected to sign a "joint action plan" for a "comprehensive strategic partnership" with China.

The visit comes at a sensitive time as China vies for diplomatic, economic and military influence in the strategically important Pacific, challenging the historic regional sway of the United States, New Zealand and Australia.

A spokesman for New Zealand Foreign Minister Winston Peters said Brown had kept the New Zealand government in the dark.

"We therefore view the Cook Islands as having failed to properly consult New Zealand with respect to any agreements it plans to sign this coming week in China," the spokesman said in a statement.

"This lack of consultation is a matter of significant concern to the New Zealand government."

Cook Islands is a small, self-governing Pacific nation that has a "free association" pact with New Zealand.

Wellington provides budgetary support and help on foreign affairs and defence to the former dependent territory, whose 17,000 people have New Zealand citizenship.

New Zealand has said that it should be consulted on international agreements that have significant strategic and security implications.

Seeing the proposed deal would allow New Zealand to "verify" whether it "presents risk to our core national interest", Peters' spokesman said.

Brown defended the visit on Thursday, saying it was aimed at expanding economic opportunities "while ensuring our sovereignty and national interests remain at the forefront".