The benchmark Nikkei stock index plummeted more than 600 points Tuesday as investors were spooked by the likelihood of further U.S. interest rate hikes and an admission by Bank of Japan Gov. Toshihiko Fukui that he has 10 million yen in an investment fund linked to insider trading.

The plunge was the Nikkei's biggest single-day point loss since the Sept. 11, 2001, terrorist attacks in the U.S.

The 225-issue Nikkei stock average fell 614.41 points, or 4.14 percent, to end the day at 14,218.60, its lowest close since Nov. 16, 2005, and its largest drop since Sept. 12, 2001, when it plunged 682.85 points.