The main All Share Price Index fell 2.79 percent (168.61 points) to 5,886.75, while the more liquid Milanka index fell 2.46 percent (129.92 points) to close at 5,145.49, according to stock exchange figures.
Turnover was 1.6 billion rupees.
Brokers said the market plunged in the morning after a brief opening rally.
People's Leasing Company, which began trading Thursday, was the most actively traded stock and closed at 17.90 rupees, 10 cents below its IPO price, with 4.3 million shares traded. The stock went up to 18.10 and a low of 17 rupees.
Transactions in John Keells Holdings accounted for the days biggest turnover with the stock closing flat at 175 rupees and over 3.3 million shares traded, including two crossings of off-market private deals each of 500,000 shares at 175 rupees a share.
Several warrants of Environmental Resources Investments were among the biggest losers of the day.
ERI's W0003 warrants closed at 13 rupees, down 2.70, W0006 ended at 13.10, down 2.50 and W0002 closed at 13 rupes, down 2.30.
Almost plantations companies traded Thursday fell, except one.
Balangoda Plantations closed at 27 rupees, down 4.50, with 131,300 shares traded.
HVA Foods, the second most actively traded share, closed at 32.70 rupees, down 4.30 with 1.26 million shares changing hands.
The government said it will go ahead with expropriation of 37 businesses deemed under-performing under a controversial new law that has been opposed by the private sector and which rating agencies have warned could deter investors.
Cabinet spokesman minister Keheliya Rambukwelle said the competent authorities have appointed with immediate effect to handle the 37 enterprises that have been taken over by the state.
Meanwhile, interest rates in overnight markets for gilt backed repos hit 8.00 percent and call rates hit a two year high of 9.25 percent and forward dollar rates also rose, dealers said.
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