Stock prices soared Wednesday on the Tokyo Stock Exchange amid speculation that U.S. investment companies are increasing their Japanese portfolios.

The benchmark 225-issue Nikkei average surged 575.06 points, or 4 percent, to end the day at 14,527.81.

There was talk that Morgan Stanley Dean Witter & Co. has doubled the weighting of its Japanese shares. The Morgan Stanley news "certainly gave the market a strong psychological boost," said Hidenori Manabe, chief equity dealer at Wako Securities Co. "Foreign brokerages have sold off stock for a long while, so signs that this may stop, even by a little, turned out to be extremely positive news."

It was the Nikkei index's strongest finish since marking 14,666.03 on Sept. 10. The broader Topix index, covering all 1,345 first-section issues, gained 41.52 points, or 3.9 percent, to reach 1,107.36. The market was closed Tuesday for a national holiday.