Russian freight trains inch across the border into Manzhouli, their cars laden with grains and oilseeds from the fertile fields of Siberia and the Russian Far East. Within days, these raw imports are cleared, processed in towering local factories, and dispatched to kitchens across China.

Manzhouli in northern China's Inner Mongolia autonomous region is the country's largest land port city. It sits opposite Russia's Zabaykalsk, where the railway crossing handles more than 60 percent of China's rail trade with Russia, making the Chinese city a critical gateway for goods moving between the two nations.

For many Russian products, Manzhouli is both the first stop in China and the launchpad for nationwide distribution after processing.

"More than 90 percent of our raw materials come from Russia," said Yang Zhihong, manager of Xin Feng Grain and Oil, a local processing company. "The supply is stable and reliable."

Inside Xin Feng's production halls, workers wash, sort and refine imported crops into flour, oils and other finished goods.

"Siberian and Russian Far East crops grow under strict ecological standards, producing nutrient-rich grains," Yang said. He added that oils and flour made from these grains sell well in the domestic market.

The company works with local residents through cooperatives. Under cross-border trade rules, each resident can enjoy a daily tax-free quota of 8,000 yuan ($1,170). The cooperatives handle the purchase and transport of imported goods to compliant grain and oil processors in Manzhouli, such as Xin Feng, where the products are processed before being sold across China.