China’s economic might has rolled up to America’s doorstep in the Caribbean, with a flurry of loans from state banks, investments by companies and outright gifts from the government in the form of new stadiums, roads, official buildings, ports and resorts in a region where the United States has long been a prime benefactor.

　　The Chinese have flexed their economic prowess in nearly every corner of the world. But planting a flag so close to the United States has generated intense vetting — and some raised eyebrows — among diplomats, economists and investors.

　　　　“When you’ve got a new player in the hemisphere all of a sudden, it’s obviously something talked about at the highest level of governments,” said Kevin P. Gallagher, a Boston University professor who is an author of a recent report on Chinese financing, “The New Banks in Town.”

　　　Most analysts do not see a security threat, noting that the Chinese are not building bases or forging any military ties that could invoke fears of another Cuban missile crisis. But they do see an emerging superpower securing economic inroads and political support from a bloc of developing countries with anemic budgets that once counted almost exclusively on the United States, Canada and Europe.

　　　　China announced late last year that it would lend $6.3 billion to Caribbean governments, adding considerably to the hundreds of millions of dollars in loans, grants and other forms of economic assistance it has already channeled there in the past decade.

　　　　Unlike in Africa, South America and other parts of the world where China’s forays are largely driven by a search for commodities, its presence in the Caribbean derives mainly from long-term economic ventures, like tourism and loans, and potential new allies that are inexpensive to win over, analysts say.

　　　　American diplomatic cables released through WikiLeaks and published in the British newspaper The Guardian quoted diplomats as being increasingly worried about the Chinese presence here “less than 190 miles from the United States” and speculating on its purpose. One theory, according to a 2003 cable, suggested that China was lining up allies as “a strategic move” for the eventual end of the Castro era in Cuba, with which it has strong relations.