The gain was stronger than the most optimistic forecast in a Reuters analysts poll.
Trade volume for private enterprises also increased, as their combined volume rose 17.8 percent, compared with the share for the same period of previous year.
China's August exports were up 5.5 percent from a year ago in dollar terms, while imports were up 13.3 percent in dollar terms.
Export growth was unexpectedly strong in the first half of the year, a positive sign for Chinese leaders who want to avoid job losses in trade-related industries as they try to nurture consumer-led economic growth.
China's total trade with North Korea between January and September rose 3.7% to US$4.03 billion, with the growth rate declining from 7.5% over the first eight months of the year.
Customs spokesman Huang Songping did not provide the trade values for September, but said imports of coal, iron ore and apparel from North Korea all declined in the month, and there were no imports of seafood.
Exports increased 12.4 percent to 11.16 trillion yuan, while imports surged 22.3 percent to 9.13 trillion yuan, the General Administration of Customs (GAC) said.
The politically volatile surplus with the United States was $28.1 billion.
BEIJING-China's exports grew for a seventh straight month in September, on continued strength in external demand for goods from the world's second-largest economy. China's economy will grow 6.8 percent this year and 6.5 percent next year, also both 0.1 percentage point higher than its July forecasts.
The cuts are expected to last through March and around 30-35 million tonnes of Chinese crude steel production could be taken offline, Commonwealth Bank of Australia analyst Vivek Dhar said in a note.
Still, while the pollution crackdown may slow China's economy and its contribution to global trade, growth in other sectors may mitigate the impact.
"There are still some infrastructure investments ongoing and some stabilisation in property investment, so I would not worry too much about the impact of environmental efforts on the growth momentum", ANZ's Wang said.