Two ships arrived in the Cook Islands in the South Pacific in March of last year. One was a familiar sight: a massive cruise ship, bringing hundreds of tourists to the pristine shores of this nation of 15,000 people. The other, a neon-orange vessel hauling complex scientific equipment, was more unusual.

On a nearby wharf, Prime Minister Mark Brown and many other prominent citizens had gathered to celebrate the smaller boat’s arrival. To Mr. Brown, the cruise ship represented his country’s troubling dependence on tourism. He described the other vessel, owned by an international mining company, as a harbinger of incredible wealth.

The Cook Islands is at the vanguard of a quest to mine the ocean floor for minerals used in electric car batteries. Mining these deposits has never been attempted on a large scale, but their reserves are so vast, proponents argue, that extracting them could power the world’s shift away from fossil fuels.

It would be a transformation for the Cook Islands, as well: Seabed mining could generate tens of billions of dollars for the tiny country, according to a 2019 study. Its per capita income is about $11,000.

But seabed mining faces stiff opposition from environmentalists, who worry that it would harm the ecology of the deep sea. More than 800 scientists have called for a moratorium on the practice, as have France, the United Kingdom and major companies like Google and BMW.

For two years, mining companies have been surveying the feasibility of seabed mining in the Cook Islands’ waters. The government is poised to decide in 2027 whether to allow it, and it faces rising pressure at home and overseas from critics who say it is rushing to embrace an untested practice.

“The government is aggressively promoting deep sea mining,” said Duncan Currie, an adviser to the High Seas Alliance and other international conservation organizations. “They seem to be pursuing seabed mining regardless of adverse effects.”

Mr. Brown insisted that the Cook Islands has not committed to mining.

The criticism “can be annoying, at times,” he said in an interview. Exploring the possibilities of seabed mining, he said, “is part of our journey of sovereign independence.”

In the past, he has pushed back against critics more forcefully.

“The very countries that destroy our planet through decades of profit-driven development, and who to this day continue their profit-driven actions, and neglect their climate change responsibilities, are making demands,” he said at a 2022 conference. “It is patronizing and it implies that we are too dumb or too greedy to know what we are doing.”

The Cook Islands, a 15-island chain that was once a colony of New Zealand, has been self-governing since 1965. Soon after achieving that status, which is short of full independence, international research vessels began exploring the country’s territorial waters, which cover about 756,000 square miles, roughly comparable to Mexico’s landmass.

The researchers found a seabed carpeted with avocado-sized rocks, or nodules, rich in cobalt and manganese. Each nodule grows the thickness of a credit card, roughly, every million years. Until recent technological advances, these rocks were unreachable.

Over the last decade, the Cook Islands has pursued those nodules in fits and starts. In 2012, it created an agency to solicit mining proposals for its own waters. In 2022, it issued permits to three companies to survey the waters and test mining technology.

Other countries that have taken steps to survey their seabeds include Japan and Norway. Most private enterprise is focused on mining in international waters, but regulations to allow this are still being hammered out.

Scouring the ocean floor, supporters argue, is the best way to obtain more of the minerals used in electric vehicle batteries and reduce the world’s reliance on fossil fuels. They add that extracting nodules from the ocean floor with proper controls would cause less environmental harm than open-pit surface mines, which often also disrupt surrounding communities.

Seabed mining — which involve crawling machines scouring the seabed, sucking up rocks and venting silt plumes — terrifies Teina Rongo, a marine biologist who runs an environmental N.G.O. in the Cook Islands’ capital, Avarua, on the island of Rarotonga.

“Our creation story is that the bottom of the ocean is where life began,” he said. “How many creatures are we going to destroy down there if we suck up all that sand?”

Mr. Rongo had just finished teaching a class about climate change for school children at a community center, where straw turtles adorned the walls and scuba gear dripped water onto the floor. Speaking to a reporter about what he called mining’s dangers, he pointed to Nauru, another tiny Pacific nation.

Rich deposits of phosphates, a fertilizer ingredient, once brought vast riches to Nauru, but mismanagement and alleged corruption plunged the nation into poverty. Now its people live in a desolate, strip-mined moonscape.

Alex Herman, the head of the Cook Islands Seabed Minerals Authority, emphasized that her agency was taking a careful, science-based approach to seabed mining. “The Cook Islands is such a special place, our own paradise,” she said, “and we want to be very mindful about any unintended consequences or impacts arising out of the progression of this sector.”

Still, some critics say Mr. Brown’s government has gotten too cozy with the companies it has allowed to survey its ocean floor. “They’ve both got the same agenda,” said Kelvin Passfield, a director of Te Ipukarea Society, a local environmental group.

Mr. Brown rejected that accusation, but critics say there has been evidence of a revolving door between the two sides.

After the former head of the mining agency, Paul Lynch, resigned, a prospecting company, Cook Islands Cobalt, hired his wife, Shona Lynch, as its top executive in the country.

Ms. Lynch defended her appointment. “I’ve got my own qualifications,” she said. “I’m not a wife that sits at home.”

Then, last year, Mr. Lynch told a local newspaper that another prospector, Moana Minerals, had taken him on a holiday aboard its survey vessel as it sailed through the Panama Canal (he compared it to a “chance to go to the moon”). Mr. Lynch, who has said that he paid for his flights, declined to comment.

Mr. Brown said he was careful not to get close to mining industry leaders. But, he added, as you “set up here, you tend to become part of the family. It’s very personal, the relationships you would have with companies.”

The government says it has put independent observers on survey ships to ensure the reliability of the companies’ data, which officials say will inform the decision about whether to pursue seabed mining.

The public appears to be evenly split over the issue, said Rashneel Kumar, the editor of Cook Islands News, the country’s largest newspaper.

But many think they know what the decision will be. Teresa Manarangi-Trott, a cautious supporter of seabed mining, led a government committee that gathered residents’ views on the practice.

“The government has decided that it’s going to happen, irrespective of what anyone says,” she said.

Reporting for this story was supported by a grant from the Peter M. Acland Foundation, a media charity based in New Zealand.