The Cook Islands announced the creation of world's largest marine park at the opening of the Pacific Islands Forum Tuesday, a vast swathe of ocean almost twice the size of France.

Prime Minister Henry Puna said the 1.065 million square kilometre (411,000 square mile) reserve "(is) the largest area in history by a single country for integrated ocean conservation and management".

Puna said protecting the Pacific, one of the last pristine marine eco-systems, was the Cooks' major contribution "to the wellbeing of not only our peoples, but also of humanity".

"The marine park will provide the necessary framework to promote sustainable development by balancing economic growth interests such as tourism, fishing and deep sea mining with conserving core biodiversity in the ocean," he said.

Australia announced in June that it was creating a network of marine parks covering 3.1 million square kilometres, more than a third of its territorial waters. However, they are dotted around its huge coastline.

The new Cook Islands protected zone will be the largest single marine park in the world, taking in the entire southern half of the nation's waters.

The nation's 15 islands have a combined landmass barely larger than Washington DC but its waters include environmentally valuable coral reefs, seagrass beds and fisheries.