At 5pm, the Thai baht also weakened to 35.61 per US dollar, a new 6-year low.
The SET index was down 36.13 points to 1,372.61 on turnover of Bt78 billion. At one point, the index was as low as 1,369 points.
"This is likely a short-term adjustment," said ASL Securities in a research note. It suggested that this is the opportunity to buy into large-cap stocks which are not affected by the tragic event like hospitals and banks.