China's politically sensitive global trade surplus narrowed by 45 percent from a year earlier to $15.2 billion.
Chinese demand has been driven by higher government efforts to reverse an economic slowdown with higher spending on railway construction and other projects.
Growth in the world's second-largest economy fell to a two-decade low of 7.5 percent in the second quarter. The latest industrial data suggest the economy gained strength in the quarter ending in September but analysts say that may not last.
"We remain cautious on the sustainability of the ongoing recovery," said JP Morgan economist Haibin Zhu in a report this week. "We expect the recovery will last until the end of the year but is likely to slow down again in 2014."
Surveys of manufacturers show barely grew in September, adding to signs a recovery might losing steam.
China's growth is generally stable but faces "pressure to decline," said Zheng, the customs official.
Chinese imports of American goods rose 16.3 percent while exports to the United States rose 3 percent. The trade surplus with the United States narrowed by 1.4 percent from a year ago to 20.8 billion.
China's trade surplus with the 27-nation European Union, its biggest trading partner, narrowed by 17 percent to $8.7 billion. Hurt by Europe's debt problems, exports to Germany fell 6.5 percent and those to France were off 2.8 percent.
The discrepancy between Saturday's export figures and forecasts also highlights complaints Beijing's data might be inaccurate and the intense focus financial markets attach to a handful of Chinese economic indicators.
In April, global stock markets fell after China's announcement its economy grew by 7.7 percent in the first quarter of the year failed to meet private sector forecasts of 8 percent. Forecasters had based their outlook on trade data they said later might be exaggerated.
Analysts believe some Chinese exporters report exaggerated values for their goods as an excuse to evade Beijing's currency controls and bring extra foreign money into the country for investment. Private sector researchers said data from its trading partners showed the value of goods from China was lower than that reported by Beijing.
The customs agency has defended its figures, saying they were based on goods that really were exported. But that would not prevent exporters from submitting inflated prices for those goods.
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General Administration of Customs of China (in Chinese): www.customs.gov.cn