The KOSPI slipped to the 6,700 level in early trade despite news that Samsung Electronics' third-quarter operating profit beat market expectations. Losses extended from the previous session as foreigners and institutions sold on a net basis.

As of 9:14 a.m. on Oct. 8, the KOSPI was down 48.62 points, or 0.71 percent, at 6,755.28 from the previous session's close.

The KOSPI opened up 4.78 points, or 0.07 percent, at 6,808.68 and then quickly slid to the 6,750 level.

Retail investors were net buyers of 323.3 billion won. Foreigners and institutions were net sellers of 260.6 billion won and 87.8 billion won, respectively, weighing on the index.

Market attention focused on Samsung Electronics' preliminary third-quarter results released before the open.

Samsung Electronics said it posted 195 trillion won in consolidated third-quarter revenue and 107.4 trillion won in operating profit. Revenue rose 13.70 percent from the previous quarter and operating profit increased 20.01 percent. From a year earlier, they climbed 126.59 percent and 782.50 percent, respectively.

Samsung Electronics shares were weaker after the results release. The stock was down 0.47 percent at 267,250 won. SK Hynix was up 0.29 percent at 1,728,000 won.

Among the top market-cap stocks, LG Energy Solution was up 3.84 percent. SK Square was down 2.19 percent, Hyundai Motor down 2.68 percent, Samsung Biologics down 2.66 percent, Samsung Life down 1.78 percent and KB Financial down 0.71 percent.

The Kosdaq also fell. At the same time, the Kosdaq was down 12.68 points, or 1.41 percent, at 885.75. It closed the previous session at 898.43.

The won was quoted at 1,337.90 per dollar, down 3.10 won from the previous session.

South Korean stocks have been weakening as foreign selling and short-term supply-and-demand factors overlap despite earnings expectations for large semiconductor shares. An analysis said volatility could increase during the session on Oct. 8 ahead of an exchange-traded fund rebalancing and options expiry, and before a market holiday on Oct. 9 for Hangul Day.

Han Ji-young (한지영), a researcher at Kiwoom Securities, said investors should watch stock moves and changes in foreign flows after the earnings release, as well as changes in 2027 profit estimates, rather than whether Samsung Electronics beat the consensus. She said meaningful changes in overall share-price moves and foreign flows in the domestic market could emerge from next week.