China is leasing an entire Pacific island. Its residents are shocked.

CHINA : The island of Tulagi served as a South Pacific headquarters for Britain then Japan, and during World War II, its natural deepwater harbor made it a military gem. Now, China is moving in with plans to effectively take control.

Under a secretive deal signed last month with a provincial government in the Solomon Islands, a Beijing-based company with close ties to the Chinese Communist Party has secured exclusive development rights for the entire island of Tulagi and its surroundings.

The lease agreement has shocked Tulagi residents and alarmed US officials who see the island chains of the South Pacific as crucial to keeping China in check and protecting important sea routes. It is the latest example of China using promises of prosperity to pursue its global aspirations — often by funneling money to governments and investing in local infrastructure projects that critics call debt traps for developing nations.

“The geography tells you that this is a good location,” said Anne-Marie Brady, a China scholar at the University of Canterbury in Christchurch, New Zealand. “China is expanding its military assets into the South Pacific and is looking for friendly ports and friendly airfields just like other rising powers before them.”

Beijing’s ambitions in the South Pacific have economic, political and military ramifications.

The region is rich in natural resources, and China’s investments have provoked worries in the United States and Australia that the projects could give Beijing an opening to establish a military foothold for everything from ships and planes to its own version of the Global Positioning System.

China is also pushing to end the region’s status as a diplomatic stronghold for Taiwan. The Solomons cut ties to Taipei and allied with Beijing just a few days before the Tulagi deal. A second Pacific nation, Kiribati, followed suit the same week.

Even compared to previous Chinese development deals in nearby countries — including a wharf in Vanuatu, whose terms were not publicly released for years — the Tulagi agreement is remarkable for both its scope and lack of public input.

The renewable 75-year lease was granted to the China Sam Enterprise Group, a conglomerate founded in 1985 as a state-owned enterprise, according to corporate records.

A copy of the “strategic cooperation agreement,” obtained by The New York Times and verified by two people with knowledge of the deal, reveals both the immediate ambitions of China Sam and the potential — just as in Vanuatu — for infrastructure that could share civilian and military uses.

Signed on Sept. 22, the agreement includes provisions for a fishery base, an operations center, and “the building or enhancement of the airport.” Though there are no confirmed oil or gas reserves in the Solomons, the agreement also notes that China Sam is interested in building an oil and gas terminal.

These are just the explicit possibilities. The document also states that the government will lease all of Tulagi and the surrounding islands in the province for the development of “a special economic zone or any other industry that is suitable for any development.”

The provincial governor who signed the deal, Stanley Maniteva, could not be reached for comment. Noting that laws and landowner rights would be respected, he told local reporters this week that the agreement had not been completed.

“I want to make clear that the agreement does not bear the official stamp of the province so it is not official and formalized yet,” he said.

But many residents of Tulagi, an island of a little over 1,000 people, are taking the signing of the document to mean it is a real agreement, and outrage has quickly set in.

“They cannot come in and lease the whole island like that,” said Michael Salini, 46, a business owner on Tulagi who is helping organize a petition to oppose the China Sam agreement.