Christian Sewing, CEO of Germany's Deutsche Bank, addresses the audience during the bank's annual meeting in Frankfurt, Germany, May 24, 2018.

Central banks "have used their tools to a large extent already" and are running out of options to mitigate the impact of global economic risks, Deutsche Bank's CEO warned on Wednesday.

The likes of the European Central Bank and U.S. Federal Reserve have "no conventional measures left to effectively cushion" the blow of a "real economic crisis," Christian Sewing said at the Sibos banking conference in London.

"I'm particularly worried about a series of financial and geopolitical risks, ranging from the situation in Hong Kong to tension in the Middle East," Sewing said, adding that the world is facing an "extraordinary macroeconomic situation that is very hard and difficult to predict, and potentially making this whole thing even more volatile."

Global central banks including the Fed and the ECB have seen a renewed focus on monetary policy easing, as concerns increase as to the health of the economy and declining inflation.

The ECB in particular has eased aggressively, lowering its deposit rate by 10 basis points to a record low of -0.5%. This effectively means lenders are charged for holding idle cash.

Sewing targeted the ECB in his speech, saying the central bank's push into negative rates runs contrary to expert opinion.

"Very few economists believe that cheaper money at this level will have an effect," Sewing said, adding that this view has been echoed by Deutsche Bank's own clients. "They will not invest an additional euro just because the loan will be an additional 10 basis points cheaper."

Sewing's comments come as the lender embarks on a huge restructuring program that pulls it out of the global equities business, sees 18,000 jobs slashed, and places a stronger emphasis on transaction banking for corporate clients.