Bangkok - The Thai stock market tumbled more than 5 per cent by midday Thursday, falling below the index's 600 watershed for the first time in four years.

The Stock Exchange of Thailand (SET) index was at 574.42 points when trading ended for the midday break, down 30.72 points or 5.08 per cent.

Like most bourses in Asia, the SET has been hard hit by the Lehman Brothers collapse and AIG bailout in the US, as both financial giants had huge operations in Asia. (dpa)