The SET index ended the day with a loss of 36.46 points or 2.41 per cent, as the new record turnover was made - Bt102.66 billion.
The exchange is unlikely to launch any measure to stem the heavy loss today.
"We will need to monitor the market closely, but I don't think weneed any measures yet," said Kesara Manchusree, president of the Stock Exchange of Thailand at a press conference.
At 2.33pm, the SET index lost 54.79 points or 3.62 per cent, to 1,460.16 points. It was last seen below 1,460 in June. On June 12, the index stood at 1,457 points.
It slid fast minutes later. At 3.27pm, the index lost 129.87 points or 8.57 per cent.
At 3.31pm, the loss widened to 135.64 points or 8.95 per cent.
At 3.39pm, the buying spree narrowed the loss to 85.56 points or 5.65 per cent. Turnover has so far reached Bt76.7 billion.
The loss has narrowed to 47.08 points or 3.11 per cent at 4.31pm. Turnover skyrocketed to Bt97.6 billion.
In the past five trading days, the index has lost 8.23 per cent. It is well below the expected 2015 price-earning ratio. Suffering the most were stocks in the energy, communications, banking, retail, property and food sectors.
The slide in Asian markets comes after crashing oil prices dragged US stocks to one of their worst losses of the year on Friday.
The Dow Jones Industrial Average fell 1.79 per cent and the S&P 500 tumbled 1.62 per cent. It was the S&P 500's first weekly loss in nearly two months and its worst single-week decline - 3.5 per cent - since May 2012.
Lower oil prices benefit consumers, but traders have been unnerved by the speed of the freefall in crude prices, which could put projects on hold in the oil sector and hurt energy companies and banks.
In Thailand, the banking and energy sectors constitute more than one fourth of the exchange's market capitalisation.
"LTF and window dressing are now the last hopes," said Asia Plus Securities in its research note. "The market slump should encourage more investment into LTF and window dressing at the end of the year should also be more active. In eight of the past 10 years, SET index gained average 2.6 per cent in the past two weeks of the year."
Technically, the index can dive further to 1,438 points, the securities house said.
This week, the US Federal Open Market Committee and Bank of Thailand will convene on policy rates. The Thai central bank is widely expected to cut the policy rate by 0.25 percentage point at this round.