The surplus rose to 15.3 billion euros ($18.8 billion) from 14.4 billion euros in April, federal statistics office Destatis said in a statement.

Economists surveyed by Dow Jones Newswires had expected the surplus to rise to 15.0 billion euros.

Exports rose by 3.9 percent to 93.5 billion euros while imports soared by 6.3 percent to 78.5 billion euros, Destatis said, citing seasonally adjusted, provisional data.

"Germany's economy is showing some strength in May. Nonetheless, we do expect the economic situation to remain volatile and remain cautious after weak data in April," said Constantin Wirschke, an economist at Natixis.

However, there were indications that the crisis was taking a toll on trade in the eurozone.

German exports to the 16 other countries that share the troubled euro were down 2.3 percent in May compared to the same month in 2011. In contrast, exports to countries outside Europe rose by 3.4 percent.

Over the five months from January to May, exports were up by 4.2 percent overall, but exports to the eurozone were down by 0.6 percent.

Germany is the world's second largest exporter after China.