Outbound shipments were likely to increase 4.1% from a year ago, after growing 7.1% in August, according to the median forecast of 30 economists in the poll.
The sluggishness of inflation, higher interest rates and the months-long Ukraine war are increasingly weighing on the global economy, with China's protracted slowdown adding to the pressure.
The official and private sector China factory activity surveys showed new export sub-indexes extended contractions last month. Exports were one of the few bright spots for the economy this year.
The PMIs add to growing evidence of a turning point in foreign demand, said Julian Evans-Pritchard, economist at Capital Economics, said this could be the beginning of a double-digit contraction in Chinese exports.
Foreign trade-related container throughput in China's eight major ports fell 14.6% in the first 10 days of September due to typhoon disruptions, but grew later during Sept. 11 - 30, according to the China Ports Harbours Association.
Imports are expected to remain weak in September, likely rising 1%, compared to only 0.3% in August.
South Korea's export growth, a leading indicator for China's imports, hit the slowest pace in nearly two years in September. Shipments from the trade-dependent country to China were down 6.5%.
In September, analysts at Goldman Sachs noted that import growth could slow down due to fewer working days and lower year-over-year growth of oil prices.
The trade surplus of China is likely to have widened with the weakening yuan to $81.0 billion, from $79.39 billion in August, according to the poll.
Trade data, which will be released on Friday, is one of the last official economic indicators to be announced before China's ruling Communist Party Congress starts on October 16. The International Monetary Fund downgraded its growth forecast for China to 3.2% from 3.3% as the world's second biggest economy struggles with continued COVID 19 curbs and a weaker property sector.