The Bank of Japan injected ¥1 trillion into money markets Friday amid a plunge in Tokyo stocks and growing global worries about dubious U.S. mortgages.

The central bank was following similar moves made overnight by its U.S. and European counterparts — the first time the central banks have acted together since the Sept. 11, 2001, terrorist attacks on the United States.

Hiroko Ota, minister in charge of economic and fiscal policy, tried to allay fears about a fallout on the Japanese financial system, calling the damage from U.S. subprime mortgages here "limited."