“It’s got a big population, the government is making it easier to enter,” said Ralf Matthaes, managing director for Vietnam and the Mekong region at TNS Global, a British market-research consulting firm, “and Vietnamese are now having that basic income level where there is not just sustainability but genuine opportunity for growth and profits.”

McDonald’s waited a long time to open in Vietnam, given its global brand recognition and likely appeal to young Vietnamese consumers. When it did, it tagged Henry Nguyen, the son-in-law of Prime Minister Nguyen Tan Dung, as its local franchisee.

Bill Hayton, a former foreign correspondent in Vietnam and the author of “Vietnam: Rising Dragon,” a 2010 book that explored links between money and power in the one-party state, said: “Laws and regulations are often rather vaguely written, giving officials plenty of opportunity to delay or assist an investor’s plans, but Mr. Nguyen has been able to negotiate these difficulties with ease. Having the second-most-powerful man in the country as father-in-law is like having a golden ticket and get-out-jail-free card all rolled into one.”

A representative for McDonald’s declined requests for a meeting or telephone interview with Mr. Nguyen, a Vietnamese-American business tycoon who moved to the United States as a child and returned with degrees from Harvard and Northwestern University to run the Vietnam office of IDG Ventures, a network of venture capital funds based in San Francisco.

In a statement, Liam Jeory, a McDonald’s vice president for corporate relations, wrote: “The contract with Henry Nguyen as developmental licensee is the result of a rigorous selection process that began years ago. Nguyen brings a strong passion for the brand that he developed while working as a part-time crew member for McDonald’s as a young student in the United States.”

Food industry experts say McDonald’s and other American fast-food brands typically market themselves in Asia as a lifestyle choice for the middle class, rather than as an inexpensive option for the poor, and that their Vietnam strategy is no exception.

Meals at a Burger King on Lo Duc Street in Hanoi were selling the other day for 65,000 dong ($3) — twice what Nguyen Thi Hang Nga charges for a bowl of pho in her restaurant across the street, where patrons sit on blue plastic stools.