The benchmark Nikkei stock average tumbled below 10,000 for the first time in 17 years Wednesday as chaos overcame world financial markets following terrorist attacks in the United States the previous day.

The 225-issue Nikkei average plunged 682.85 points -- more than 5 percent -- to close at 9,610.10. It hit a session low of 9,604.40 during the morning, down 688.55 points. The Nikkei last closed below 10,000 on Aug. 1, 1984.

The dollar was also affected. It fell from near 122 yen to around 118 yen in overseas markets following the attacks, then hovered at the 119 yen level in Tokyo on Wednesday amid thin trading.