South Korean stocks closed lower Thursday, roiled by an overnight Wall Street tech plunge and vaccine concerns amid uncertainties over the quadruple expiration of key stock derivatives. The Korean won rose against the US dollar.

After choppy trading, the benchmark Korea Composite Stock Price Index (KOSPI) fell 9.01 points, or 0.33 percent, to close at 2,746.46.

Trading volume was high at about 1.2 billion shares worth some 20.3 trillion won ($18.6 billion), with gainers outnumbering losers 659 to 192.

The KOSPI retreated after a 2.02 percent gain the previous session, led by massive foreign selling.

Foreigners dumped a net 1.4 trillion won, while retail investors purchased a net 893 billion won. Institutions bought a net 442 billion won.

The KOSPI's fall was led by shares in tech giants, tracking a 1.94 percent overnight plunge on the Nasdaq composite. The US Federal Trade Commission's antitrust lawsuit against Facebook curtailed investor appetite for tech heavyweights.

Volatility remained high the entire session, with the KOSPI plunging over 1 percent in the morning and briefly spiking to another all-time high in the afternoon.

Analysts said uncertainties increased on "the quadruple witching day," or the expiration day of four key derivatives, including KOSPI-tracking options and futures.

"Sell-offs increased from the quadruple witching day, but strong individual buying buffered the KOSPI's further plunge," said Bookook Securities researcher Lee Won.

In Seoul, most large caps closed lower.

Market bellwether Samsung Electronics lost 1.35 percent to 72,900 won, and No. 2 chipmaker SK hynix shed 3.32 percent to 116,500 won.

Top pharmaceutical firm Samsung Biologics retreated 0.36 percent to 819,000 won, while Celltrion gained 1.84 percent to 360,000 won.

Internet portal giant Naver declined 0.69 percent to 286,000 won, with its rival Kakao down 1.2 percent to 370,500 won.

Leading chemical maker LG Chem fell 2.27 percent to 817,000 won, and rechargeable battery maker Samsung SDI dropped 1.06 percent to 560,000 won.

Hyundai Motor, the country's largest automaker, closed unchanged at 191,500 won, and top steelmaker Posco dropped 0.37 percent to 272,000 won.

The local currency closed at 1,187.7 won per dollar, up 2.9 won from the previous session's close.

Bond prices, which move inversely to yields, closed lower. The yield on three-year Treasurys rose 0.7 basis point to 0.966 percent, and the return on the benchmark five-year government bond added 0.7 basis point to 1.318 percent. (Yonhap)