The Cook Islands lie halfway between New Zealand and Hawaii and are made up of 15 islands and atolls.
Western nations that traditionally held sway in the Pacific Islands have become increasingly concerned about China's plans to increase influence after Beijing signed defence, trade and financial deals with Pacific countries in recent years.
"The Government of the United States of America has begun discussions with the Government of the Cook Islands to support the research necessary to inform seabed exploration and responsible development within the Cook Islands' Exclusive Economic Zone," the State Department said in a statement.
US-linked firms "sit at the forefront" of deep seabed mineral research and exploration in the Cook Islands, it said.
In June, New Zealand suspended millions of dollars in budget funding to the Cook Islands after its prime minister signed partnership agreements with China without consulting Wellington.
Those agreements committed them to deepening co-operation in seabed mining as well as education, the economy, infrastructure, fisheries and disaster management.
On Wednesday, New Zealand's foreign ministry said it was aware of the new arrangement with the US and respected "the rights and responsibilities of states to manage their mineral resources".
The Cook Islands were within New Zealand's borders from 1901. In 1965, the country became self-governing but in free association with New Zealand. The constitutional ties require the two countries to consult on security, defence and foreign policy.
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