Huge areas of seabed around the Cook Islands are carpeted in polymetallic nodules, lumpy rocks studded with rare earths and critical minerals such as cobalt, nickel and manganese.

With existing supplies of critical minerals heavily exposed to trade disputes, both the United States and China have signalled an interest in deep-sea mining.

The Cook Islands said Wednesday it had agreed to work with the United States on the "responsible development" of its seabed riches.

"Both countries agreed to cooperate further in the responsible management of seabed minerals, with a committment to scientific advancement, mutual prosperity, economic self-reliance, and environmental stewardship," the government said in a statement.

The US Department of State said it had started discussions with the Cook Islands to support deep-sea exploration efforts.

"Seabed minerals are critical for developing and powering the technology of today and the future," it said in a statement.

US President Donald Trump earlier this year signed an executive order targeted at "unleashing" mineral resources found in the deep ocean.

Critical minerals such as cobalt and nickel are in hot demand for electric vehicles, rechargeable batteries and advanced military technology.

The Cook Islands -- which lays claim to one of the world's biggest deposits of polymetallic nodules -- signed a contentious deep-sea mining cooperation deal with China earlier this year.

That deal angered the Cook Islands' former colonial ruler New Zealand -- a key US ally in the region -- which complained of being blindsided.

New Zealand halted aid to the Cook Islands in June after it signed a string of agreements with China, including the deep-sea mining deal.

Cook Islands' Pacific neighbour Kiribati is also exploring a deep-sea mining deal with China.

While exploration for deep-sea mining is far advanced, no company or nation has started production on a commercial scale.

Critics fear deep-sea mining will smother marine life with plumes of waste, and that the alien noise of heavy machinery will disrupt oceanic migrations.