In the morning session, the index nosedived for the third day in a row, plunging by 79.12 points. or 5.52 per cent to 1354.35 points.
Thailand is not the only loser. In the morning session, Japan fell by 6.35 per cent, followed by Philippines (5.52 per cent), Taiwan (2.03 per cent), and South Korea (1.42 per cent).
SET President Charamporn Jotikasthira said the exchange has informed the Finance Ministry and the Bank of Thailand of the plunge, which is attributable to heavy selling spree by foreign investors.
Foreign funds are returning to the US after some economic indicators showed improvement and may encourage the Federal Reserve to taper the quantitative easing.
He believed that if the global economy would benefit if the US economy could achieve sustainable recovery. However, foreign capital outflows would continued in a short while. He insisted that there would be no measure to block capital outflows.
Losses in the previous two days have already narrowed the year-to-date gain from more than 20 per cent in mid-May and 12.22 per cent at the end of May to just 2.98 per cent. Foreign investors this month have been the net sellers of Thai shares. Yesterday, their net sells were worth Bt6 billion, boosting month-to-date net sells to Bt34 billion and the year-to-date figure to Bt55 billion.
According to Asia Plus Securities, in the past 14 trading days, foreign investors were net-sellers in 13 days with combined net-sells of Bt51.5 billion. Average daily net-sells totalled Bt3.6 billion.
"This is the heaviest sell-offs, much higher than after the Hamburger crisis in 2008," it said in a research note.