"It looks like it will be a close result, as expected. However the vote of the Turkish people turns out in the end, we'd be well advised to keep calm and to proceed in a level-headed way," Foreign Minister Sigmar Gabriel said in a statement.
"It's good that election campaign, which was fought so bitterly, including here in Germany, is now over," said Gabriel, a member of the Social Democrats (SPD) - the junior partner in Chancellor Angela Merkel's ruling coalition.
Peter Altmaier, Merkel's chief of staff, said on German broadcaster ARD that the result showed there was a "very lively political debate" in Turkey but said it was necessary to wait for official results before commenting further.
He said there were election observers in Turkey and the German government "would of course respect a result that came about in a free and democratic vote".
Asked if the vote was free and democratic, Altmaier said the German government would discuss the result once it was official and election observers would look at whether it was fairly conducted.
Senior SPD member Axel Schaefer said majorities reached in democratic votes could turn against democracy itself, pointing to the 1933 elections in Germany, when support for Adolf Hitler's Nazis surged.
"The Brexit vote is pushing Britain into the sidelines, the presidential election of (U.S. President Donald) Trump is taking the USA on an adventure, the Erdogan referendum is leading Turkey into absolutism and the 1933 German parliamentary election led Germany into the abyss," he said.