The decline was steeper than the drop of 3 per cent that was the median estimate of 11 economists polled by The Wall Street Journal. It was also the eighth month out of the past nine in which exports fell, with November's small increase the exception.
Chinese exports fell last month owing to weak demand in many major markets, and the government and economists are bracing for further difficulties this year given the prospect of a more protectionist Trump administration.
Imports in December rose 3.1 per cent from a year earlier, roughly in line with expectations, compared with a 6.7 per cent gain in November. China's trade surplus narrowed last month more than expected to US$40.82 billion from $44.61 billion in November.
Overall in 2016, exports fell 7.7 per cent and imports declined 5.5 per cent, resulting in an annual trade surplus of $510 billion, below the $594.5 billion trade surplus in 2015.
Chinese exports saw slipping demand across all major regions except the US, which saw a 5 per cent increase, according to the customs data. "Overall, exports will face challenges over the next couple of quarters," said RHB Group economist Fan Zhang. He said it is very likely a Trump administration will "play hardball" with China.
Ministry of Commerce spokesman Sun Jiwen cited mounting protectionism as a challenge and said that Beijing will "try all methods" to stabilise trade, including steps to help exporters expand foreign markets and become more competitive.
Companies too said that they're feeling the pinch and are concerned that trade tensions lie ahead.
Beijing has allowed China's currency to fall against the dollar - it depreciated 7 per cent last year - but the yuan appreciated 1 per cent in 2016 against a trade-weighted basket of currencies.
Some economists said China is unlikely to issue a foreign trade growth target this year for the second year in a row after missing its benchmark by wide margins in 2013, 2014 and 2015.