The rise beat the poll's forecast for a 15% gain.
Exports rose 8.1 percent to $198.3 billion, up from August's 5.5 percent, trade data showed Friday.
Trade figures in dollars will be released later in the day.
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. Trade surplus shrank 28 percent to 193 billion yuan.
The value of service imports gained 12.2 percent year on year to 2.13 trillion yuan (more than 320 billion US dollars) in the January-August period, while exports only increased 4.4 percent to 926.69 billion yuan, resulting in a 1.2-trillion-yuan deficit, the Ministry of Commerce (MOC) said Thursday in a statement. The surplus grew to $28.08 billion from $26.23 billion in August.
China's exports expanded at a slower than expected pace but remained robust in September. 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.
Authorities are in the midst of a campaign to reduce the risks from a rapid build-up in debt produced by years of credit-fuelled stimulus, and sustained trade growth could give policymakers confidence to step up the campaign next year once the leadership reshuffle is out of the way.
"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.