Export numbers have been buoyed by producers rushing to fill orders before American tariffs rose, but they also benefit from "robust USA demand" and a weaker Chinese currency, which makes their goods cheaper overseas, said Louis Kuijs of Oxford Economics in a report.
Communist officials have ordered companies to stop buying American soybeans - the biggest US export to China - and find alternative suppliers and export markets for other goods.
The volume of exports from China to Russian Federation has grown by nearly 13 percent, exceeding $35 billion.
Analysts said last month's strong export growth - which might indicate US tariffs are not biting much yet - is unlikely to be sustained.
Exports jumped 14.5 percent for September on-year, beating forecasts from analysts polled by Bloomberg News, while imports rose 14.3 percent on-year.
"The big picture is the Chinese exports have so far held up well in the face of escalating trade tensions and cooling global growth, most likely thanks to the competitiveness boost provided by a weaker renminbi (yuan)", said Julian Evans-Pritchard, China economist at Capital Economics.
Lowered manufacturing output reported at the end of September in China indicates that the tariffs may be starting to bite Beijing.
"The front-loading impact is quite obvious to me", said Betty Wang, senior China economist at ANZ in Hong Kong.
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"If that's the case then I think further downside risk can be expected in the fourth quarter", Wang said.
"They want to negotiate, they want to negotiate badly, but I told them, 'You're not ready yet". Imports of Russian goods surged by around 40 percent to $42 billion, said the customs service.
Indeed, analysts expect the trade imbalance to continue to widen over the next few months before the next round of American tariffs kick in, in no small part because the divergence in consumer demand in the two countries.
China's trade surplus with the United States was $225.79 billion from January-September.
Growth in China's factory sector in September stalled after 15 months of expansion, with export orders falling the most in more than two years, a private business survey showed.
Imports of American goods increased 9 percent to $12.6bn, down from 11.1 percent.
The president and Vice President Mike Pence in recent weeks have also accused Beijing of trying to meddle in November's midterm elections to hurt Trump because he is putting pressure on China over trade.