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.

At 5 p.m., the dollar was quoted at 119 yen.36-39, compared with 119 yen.35-45 at 5 p.m. in New York on Tuesday. It traded at 121 yen.71-73 in Tokyo late Tuesday.

The dismal Nikkei figures present a stark contrast to the Nikkei's record closing high of 38,915.87, set in December 1989 at the height of the bubble economy.

The broader Tokyo Stock Price Index of all first-section issues sank 67.32 points to finish the day at 990.80. It hit 993.15 at midmorning, dipping below 1,000 for the first time since Oct. 16, 1998. The Topix last closed below 1,000 on Oct. 15, 1998, when it ended at 980.11.

The market opened at 9:30 a.m., 30 minutes later than usual, to give investors time to place orders following steps by the Tokyo Stock Exchange to restrict price fluctuations in the wake of the terrorist attacks.

Tokyo stocks fell sharply across the board, with 658 issues hitting new lows for the year. The plunge came in the wake of a tumble in European markets on Tuesday. U.S. markets, shut down Tuesday following the attacks, remained closed Wednesday.

The airline sector led the fall, posting a 10.38 percent loss. Investors viewed hijacked airplanes as an extremely negative factor.

Japan Airlines hit a new low for the year.

Shares in firms heavily dependent on U.S. sales suffered aggressive sales.

Sony spent the entire day at ask-only and closed at 4,730 yen, falling 250 yen, its daily limit. The figure was the firm's lowest close in 2001.

Chief Cabinet Secretary Yasuo Fukuda attributed the Nikkei's tumble to "an extremely abnormal reason," in a morning news conference.

However, market players criticized the government's attempt to play down the stock price tumble.

"It is problematic that the government is using the attack as an excuse for the Nikkei's falling below 10,000," said Yuji Ono, a manager at the equity division of Nikko Securities Co.

Ono said market players believe the sagging Japanese economy and slow government policymaking are the core factors behind the tumble.

Fukuda, the top government spokesman, asked market players to react calmly to the financial chaos, which sparked heavy selling in European markets on Tuesday. U.S. markets will remain closed on Wednesday.

The TSE and other bourses in Japan halved the maximum daily stock price fluctuation range, a measure to prevent violent fluctuations in the wake of the attacks.

Remain calm: TSE

The president of the Tokyo Stock Exchange on Wednesday urged investors and brokerage houses to stay calm in the wake of the devastating terrorist attacks on the United States.

"We urge investors to behave in a discreet manner and brokerage houses to operate in a discreet and appropriate manner," Masaaki Tsuchida said in a statement.

"Given the unstable situation in the market, we also urge them to refrain from taking any action that may undermine credibility in the market, such as spreading rumors," he said.

In a similar statement, Eiichiro Okumoto, chairman of the Japan Securities Dealers Association, said he expects the association's member brokerage houses to operate in a discreet manner and to encourage investors in an appropriate way.

The statement noted that the association commenced Wednesday's trading of its Jasdaq over-the-counter market at 9:30 a.m. instead of 9 a.m.

The Tokyo Stock Exchange also delayed the start of Wednesday's trading until 9:30 a.m.