TOKYO, March 22 (Reuters) - The 30-year Japanese government bond yield struck a record low on Tuesday as the flattening of the curve continued amid persistent investor demand for debt that still offer positive yields.

The JGB yield curve through the 10-year maturities now yield below zero percent, dragged down under the Bank of Japan's negative interest rate policy.

The 30-year yield touched 0.455 percent on Monday, an all-time trough.

(Reporting by Shinichi Saoshiro; Editing by Kim Coghill)