(Adds details, updates yield moves)
TOKYO, March 8 (Reuters) - Japanese government bond yields tumbled to fresh record lows on Tuesday after a firm 30-year auction fuelled a rally for debt instruments that still offer positive yields, which have become scarce under the Bank of Japan's negative interest rate policy.
Weaker Tokyo stocks also increased the allure of the bond market, with the Nikkei falling to a one-week low.
The benchmark 10-year yield fell to a new record low of minus 0.100 percent.
The 30-year yield plummeted 21 basis points, the biggest one-day fall in three years, to a life-time trough of 0.470 percent.
The rally by super long JGBs was triggered by strong results in a 30-year auction, underlining solid investor demand for the maturities that offer positive yields but also entailing greater duration risk.
"There were some concerns that the 30-year auction may not garner sufficient demand and the firm results prompted a rally in the bond futures. The auction results show domestic banks' JGB buying is extending towards the super longs," said a dealer at a Japanese financial institution.
The BOJ adopted negative interest rates in January in its latest attempt to shore up the Japanese economy, prompting a drop in bond yields. JGBs with maturities of up to 11 years are now trading at negative yields under the central bank's negative rates policy.
Domestic banks were previously not the main players in the super long 20-year and 30-year JGBs, traditionally dominated by life insurers and pension funds. But banks' hunt for yields has taken them to the super longs bond yields through much of the curve now below zero.
The bid-to-cover ratio, a gauge of demand, at the 800 billion yen ($7.08 billion) 30-year offering was a strong 4.21, compared to 3.04 from the previous sale in December.
($1 = 112.9800 yen) (Reporting by the Tokyo markets team; Editing by SImon Cameron-Moore & Shri Navaratnam)