Germany's trade surplus shrank in May as exports declined unexpectedly, official data showed on Friday, pointing to possible clouds on the horizon for Europe's biggest economy.

The trade surplus is a key gauge of an economy's comparative strength and in recent months has highlighted Germany's robustness amid the current global economic uncertainties. But it declined in May owing to lackluster exports, according to data published by federal statistics office Destatis. Together with disappointing industrial output and factory orders data earlier this week, analysts said the German economy could be slowing after solid growth in the first quarter.

German exports declined by 1.8 percent to 99.5 billion euros ($110 billion) in seasonally adjusted terms in May, Destatis said. Analysts had been projecting an increase of around 0.5 percent in exports for that month.

At the same time, imports - a measure of domestic demand - edged up 0.1 percent to 77.4 billion euros.

That meant that the trade surplus - the balance between exports and imports - contracted sharply to 22.2 billion euros in May from 24.1 billion euros in April, the statisticians calculated.