China's monthly trade data has shown exports fell in April from a year ago by 6.2% in yuan terms compared to expectations for a rise of about 1.5%.
Imports also fell for the month by 16.1% in yuan terms, compared with forecasts for a fall of about 12%.
That means the country's trade surplus has risen to 210.2 billion yuan (£21bn; $32.4bn) from 18.6bn yuan in March.
Recent economic data from the mainland has shown further signs that China's slowdown is continuing.
"[The surplus rise] was mainly due to further import weakness," said Moody's analyst Alistair Chan in a note.
"Imports have slowed on account of the housing slump and reduced demand for commodities, while exports have been softened on account of the uneven global recovery," he said.
Economist Tony Nash of Delta Economics said there was clearly pressure on China's trade environment.
"But the environment is improving and will continue through the second quarter," he said. "We see some difficulties in the third quarter, with recovery late in the year."
In US dollar terms, China's exports for the month fell 6.4%, while imports fell 16.2%, and the trade surplus rose to $34.13bn.
Some official numbers from the mainland are now reported by media in both currencies, because of currency conversion factors based on US dollar and Chinese yuan movements over the last year.
China's economy grew by 7.4% in 2014, its weakest for almost 25 years.