South Korea's key stock index tumbled more than 1.5 percent Thursday amid virus concerns and uncertainties from the expiration of options and futures. The Korean won fell against the U.S. dollar.

The benchmark Korea Composite Stock Price Index (KOSPI) dipped 48.29 points, or 1.53 percent, to close at 3,114.7 points.

Trading volume was moderate at about 910 million shares worth some 17.3 trillion won ($14.8 billion), with losers outnumbering gainers 655 to 214.

Foreigners sold a net 318 billion won, and institutions offloaded a net 935 billion won, while retail investors bought 1.2 trillion won.

The KOSPI opened sharply lower as South Korea's daily coronavirus cases remained in the 2,000s for the second straight day Thursday despite the highest level of virus curbs in most parts of the country.

Health authorities warned new infections may further increase ahead of the Chuseok holiday, which runs from Sept. 18-22 this year. Millions normally travel across the country for family gatherings over the autumn harvest holiday.  

Stock prices partially fell from the influence of the quadruple expiration of futures and options.

"Uncertainties from the expiration day for stock options seem to have stretched the KOSPI's losses, particularly driving down most of the large caps," Mirae Asset Securities analyst Park Gwang-nam said.

Market bellwether Samsung Electronics lost 1.31 percent to 75,300 won, and No. 2 chipmaker SK hynix declined 2.83 percent to 103,000 won.

Internet portal operator Naver retreated 2.56 percent to 399,000 won, and its rival Kakao plummeted 7.22 percent to 128,500 won in the wake of the ruling Democratic Party lawmakers' criticism over the market dominance of giant platform businesses.

Top automaker Hyundai Motor decreased 2.11 percent to 208,500 won, and leading chemical firm LG Chem lost 1.06 percent to 748,000 won.

Pharmaceutical giant Samsung Biologics dropped 1.93 percent to 913,000 won, while bank top cap Kakao Bank moved down 0.41 percent to 72,000 won.

The local currency closed at 1,169.2 won against the US dollar, down 2.5 won from the previous session's close. (Yonhap)