A massive selloff on the Tokyo Stock Exchange wiped out some 23.5 trillion yen ($287 billion) from the market's value on Monday with investors dumping stocks as the country recoiled from a devastating earthquake and struggled to avert nuclear disaster.

The selloff triggered record volumes and slashed the market's value to roughly 289 trillion yen.

The Nikkei average tumbled 6.2 percent, its biggest decline in a single day since October 2008, and more than 4.88 billion shares changed hands on the exchange's first section, the highest number since World War 2.

Volume was pushed up by window-dressing selling by domestic institutional investors for the March 31 financial year-end and by domestic investment trusts and anxious retail buyers, while long-term foreign players who have piled into Japanese shares since November also rushed for the exit, market players said.

It's the end of the business year for Japanese institutions. They've been net sellers of Tokyo stocks anyway, and in March they traditionally lock in profits for the year, so much of today's selling pressure likely came from them, said Mitsuhsige Akino, a fund manager at Ichiyoshi Investment Management.

On the other hand, foreigners had bought over 2.75 trillion yen worth of Japan stocks since November, pushing the Nikkei several percent higher, so no wonder they tried to trim their losses or lock in as much profit as possible today, and that bolstered trading volume said Akino.

Fears of more quake aftershocks and further repercussions from damaged nuclear reactors were cited as the most important factors behind the sell-off.

Domestic investment trusts and funds are dumping everything today. Sell orders for tens of billions of yen were detected, said an equities trader at a Japanese domestic institutional investor, who declined to be quoted by name.

Individual investors, who often trade in smaller stocks on the TSE's Mothers section for startups, likely sold even more aggressively then the big players on the Nikkei, traders said.

The Mothers market tumbled 17.2 percent, with social networking site Mixi Inc. and Japan's third-biggest airline Skymark Airlines Inc both down around 18 percent. ($1 = 81.915 Yen)

(Reporting by Antoni Slodkowski and Hideyuki Sano; Editing by Michael Watson)

Japan Tokyo Stock Exchange Quake