The Tokyo Stock Exchange shut down trading early to avoid system troubles Wednesday amid a continued free-fall as investors spooked by the investigation into Livedoor Co. flooded the bourse with sell orders.

The benchmark Nikkei 225 index dropped 464.77 points to close at 15,341.18 points, its biggest drop since May 10, 2004. The plunge came on the heels of the 462.08-point dive Tuesday. The key average briefly plummeted more than 700 points.

At 1:21 p.m., the Nikkei average was down 746.43 points, or 4.7 percent, at 15,059.52. However, it resisted a further fall and managed to stay above the 15,000 line.