German investor confidence dropped sharply in September according to a closely-watched survey, amid concerns of weaker demand for exports.

The ZEW institute said Tuesday its indicator of economic sentiment fell to 12.1 points in September from 25 points in August, well below its long term average of 24.9 points and its sixth monthly drop in a row.

ZEW chief Clemens Fuest says a weakening in developing economies has dampened the outlook for Germany's export-driven economy.

The poll of 220 financial experts showed a rise in their assessment of the current situation, up 1.8 points to 67.5.