Updated

A survey is showing a sharp rise in German investor confidence, with falling oil prices and a weaker euro among factors fueling optimism in Europe's biggest economy.

The ZEW institute said Tuesday that its monthly index, which measures investors' economic outlook for the next six months, spiked 23.4 points to 34.9 in December. That was the second consecutive increase and took the index above the long-term average of 24.4.

ZEW also said investors' assessment of Germany's current situation also improved.

Recent data have showed a promising increase in German factory orders, though the central bank has cautioned that it expects only modest economic growth over the winter.

ZEW president Clemens Fuest cautioned that "the current optimism is fuelled by factors that might change even over the short term."