Tokyo - Japan's key Nikkei 225 Stock Average fell more than 5 per cent in Thursday morning trading as the market sentiment was dampened due to persistent worries over the US economy and the yen trading stronger against other currencies.

The Nikkei index tumbled 5.12 per cent, or 445.46 points to 8,250.05.

The broader Topix index of all first-section issues also fell 36.84 points, or 4.21 per cent, to 838.39.

Exporters were hurt by the stronger yen as it shaves off Japanese firms' earnings overseas.

On currency markets at 9 am (0000 GMT), the dollar fell to 94.78-83 yen from Wednesday's 5 pm quote of 97.94-97 yen.

The euro was quoted at 1.2455-60 dollars, down from Wednesday's 5 pm quote of 1.2603-06 dollars, and 118.05-15 yen, down from 123.46-50 yen. (dpa)