New Zealand expressed renewed concern on Monday about the Cook Islands' prime minister travelling to China this week to sign agreements without properly consulting with Wellington despite the two nations' constitutional ties.

China is insisting that a visit this week by the prime minister of the Cook Islands to Beijing is not meant to conspire against anyone in the South Pacific. But the trip is creating a diplomatic dispute between the tiny nation and its chief financial supporter,

But the proposed pact has shaken decades-old ties between the Cook Islands and New Zealand, neighbours that are set to mark 60 years of a free association agreement in 2025. That agreement has long given New Zealand influence over the Cook Islands, especially over its foreign policy.

Diplomatic storm clouds are gathering around the Cook Islands, a picturesque tourist destination in the South Pacific known for its creaking palms, pink beaches and deliciously warm nights.

Concerns are mounting in New Zealand as the Cook Islands’ Prime Minister travels to China this week to sign agreements without properly consulting with New Zealand, despite the two nations' constitutional ties.

New Zealand, along with Australia and the United States, have become increasingly concerned about China’s growing presence in the Pacific region.

"The relationship between China and the Cook Islands does not target any third party," the Chinese Foreign Ministry says, as opposition leaders in Rarotonga plan protest.