The atmosphere is more bizarre than menacing, and none of the people questioned on either side of the border expressed any worries about safety. Shao Yuqun, a Chinese construction worker laboring in the snow, said he was far more anxious about frostbite than Islamist terrorism. Like many Han Chinese living in Xinjiang but originally from the other side of the country, he said he had migrated west because he could earn more than at home.

The border-straddling zone, known as the International Center for Boundary Cooperation and located just a few miles from a new Kazakh railway hub for freight trains from China, was meant to become an island of trade-driven prosperity that would showcase Kazakh-Chinese cooperation and help enrich both countries’ impoverished border areas.

Instead, it has become a study in the wide economic gulf that has opened up between a booming China, which used to look up to the Soviet Union as its “big brother,” and struggling former Soviet lands.

Compared with most other former Soviet republics, Kazakhstan is faring reasonably well, its economy driven by a highly educated population and large reserves of oil and other natural resources. Ruled by Nursultan A. Nazarbayev for its 26 years of independence, the country has avoided the violent strife that has cursed other former Soviet lands in Central Asia. It is deeply corrupt and hardly a thriving democracy, but it is far less intrusively authoritarian than China.