Asian stocks tumbled, driving the benchmark index to its lowest level since November 2005, on concern credit market losses will increase and slowing growth will damp demand for the region's exports.

Mitsubishi UFJ Financial Group Inc and Australia & New Zealand Banking Group Ltd fell more than 4 percent after Lehman Brothers Holdings Inc posted a wider loss than analysts estimated. Mazda Motor Corp, which gets more than half of its operating profit in Europe, plunged the most in seven years after the European Commission cut the euro area's growth outlook. Sumitomo Heavy Industries Ltd retreated 5.3 percent after Japan's machinery orders declined.

The MSCI Asia Pacific Index sank 2.6 percent to 114.74 as of 7:35 pm in Tokyo, set for its biggest loss since July 25. The measure has given up gains made in a Sept 8 rally sparked by the US government's takeover of Fannie Mae and Freddie Mac.