TOKYO -- Japan's central bank now holds over 300 trillion yen ($2.44 trillion) in Japanese government bonds as a result of long-term monetary easing measures -- a development that is raising fears of market volatility.

The Bank of Japan's bondholdings as of last Thursday equaled around 60% of the nation's gross domestic product, figures released Monday show. That ratio is up from slightly under 30% in April 2013, when the central bank began massive quantitative and qualitative easing measures. Most European and U.S. central banks hold the equivalent of around 20% of their country's GDP in bonds.