Japan's central bank has pumped two trillion yen (£14.6 billion) into money markets after global stocks hit major turbulence on escalating European debt fears and a record plunge on Wall Street.
The emergency infusion was the first since December 2 and is intended to calm nerves as stock markets tumbled and the yen appreciated sharply overnight.
The benchmark Nikkei 225 stock average fell 3.7% to 10,295.63 in early trade on Friday.
"We would like to ensure stability in financial markets by providing ample funds to banks," Bank of Japan official Yuichi Adachi said.
Investors dumped shares across the board in Asia after the Dow Jones industrials plunged 1,000 points at one point on Thursday - the biggest drop ever during a trading day - amid fears that Greece's debt problems could halt the global economic recovery.
A technical glitch is suspected of contributing to the plunge.