China exported and imported many more goods in September than analysts expected, according to Chinese data published Monday, driven largely by improving economic conditions in the U.S. Exports were 15.3 percent higher than last year, while imports rose 7 percent, amounting to a $31 billion trade surplus for the month.

“The strength seems to have been driven by a surge in imports for processing and re-export,” Julian Evans-Pritchard, China economist for Capital Economics, said in a note Monday. “As such, it mostly reflects a brighter export outlook rather than a pick-up in domestic demand.”

The news comes as China’s economy struggles to maintain growth, with weak factory activity and easing domestic demand amid a struggling property market.

Analysts had expected China’s exports to rise by 12 percent and imports to fall by 2 percent from last year, according to Bloomberg consensus estimates. Exports rose 9.4 percent from August, and imports rose 8.5 percent sequentially.

Imports rose as factories processed and reshipped goods such as Apple Inc.'s iPhone 6 unveiled last month, reflecting stronger foreign demand and not necessarily improving consumer spending in China.

“Looking ahead, we expect exports to remain healthy as global growth continues to recover, largely on the back of improving conditions in the US,” Evans-Pritchard said. “Meanwhile, we expect the surge in import growth to prove short-lived.”