Doctoroff's experience of running New York City is a timely reminder to Chinese policymakers who are obsessed with controlling the size of the nation's largest cities. Concerned about the increasing pressure of congestion, pollution and water shortages as results of a rapidly growing population, Beijing is considering moving some of its functions to neighboring Hebei province.

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But many city planning experts said they worry the "sprawling city" problem would be aggregated, and argued that compared with cities like New York and Tokyo, Beijing is far less dense.

Reluctant to engage in the argument, Doctoroff said it is unwise to assume what works in a city might work in another. But he also said he is a firm believer that immigrants are a positive contributor to a city.

With 40 percent of population born outside of the United States, and about 150,000 immigrants coming to the city every year, New York is perhaps the most immigrant-friendly city in the world. But Doctoroff said in his view, immigrants generate more revenue to the city than they actually consume, which is critically important for the prosperity of the city.

"One thing that we have not done is concentrating immigrants in any particular places. They live throughout the city. They live where they can find housing, gain access to social service, which the city largely pays for," he said.

But what New York does differs from Chinese cities. The city government, for example, doesn't cover much of the bill for residents' medical care, must of which is reimbursed by the central or state governments.

In the US, national health coverage programs such as Medicare and Medicaid offer an environment that allows national labor mobility, while in China local governments shoulder a large share of the healthcare burden, which reduces their willingness to absorb immigrants.

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