China's monthly trade data shows exports fell in March from a year ago by 14.6% in yuan terms, compared to expectations for a rise of more than 8%.
Imports meanwhile fell 12.3% in yuan terms compared to forecasts for a fall of more than 11%.
The numbers mean the country's monthly trade surplus has shrunk to its smallest in 13 months.
China's economy grew by 7.4% in 2014, its weakest for almost 25 years.
Analysts said recent indicators showed further signs the slowdown is continuing.
In US dollar terms, China's exports for the month fell 15%, while imports fell 12.7%.
Currency conversion factors based on US dollar and Chinese yuan movements over the last year mean some official numbers from the mainland are now reported in both currencies.
The official March data leaves the country with a monthly trade surplus of 18.16bn Chinese yuan ($2.92bn; £1.99bn).
In February, China's monthly trade surplus hit a record $60.6bn, as exports grew and imports slid back.
Analysts said the export numbers for March were a surprise.
"We can understand the imports fell because of falling imports of commodities, but exports fell so much, it was very much unexpected," said Shanghai-based analyst Nie Wen from Hwabao Trust.
However, he said one major reason for the falling exports was yuan appreciation.
Tony Nash, global vice president of Delta Economics, said the numbers took in the lunar new year period which was typically a bit volatile.
"We usually average February and March to get a true picture of what's actually happening," he told the BBC.
"If we look at February's 48% rise in exports and March's 15% fall in exports, we get a moving average of 16.7%, which is closer to where we've seen exports over the past two months."
But Mr Nash said Delta Economics was expecting a further slowdown going forward.
"In the second quarter, we'll look for an average of 9.9% year-on-year export growth and 11.7% import growth," he said.
"Trade will fall towards the back half of the year and we will look for average export growth in 2015 at 8.7% year-on-year, and import growth at 10.3% year-on-year.