A financial data screen in Shinhan Bank's dealing room in central Seoul displays figures for the Kospi, Samsung Electronics, SK hynix and Hyundai Motor during trading on Tuesday. (Yoon Chang-bin/The Korea Herald) The South Korean benchmark Kospi slumped during intraday trading Tuesday, despite market heavyweight Samsung Electronics posting a record-high quarterly operating profit earlier in the day.The benchmark index opened 1.64 percent lower at 7,919.20, before extending its losses to below the 7,400 mark, dipping to as low as 7,389.22. As of 2:50 p.m., the Kospi was trading at 7,582.69, down 5.82 percent on-session.Earlier in the session, a sell-side sidecar was triggered at 10:23 a.m., suspending program sell orders for five minutes. The measure was followed by a market-wide circuit breaker at 1:51 p.m., which halted trading on the main bourse for 20 minutes.Tuesday's plunge caught the market by surprise, as market heavyweight Samsung Electronics reported a record quarterly operating profit of 89.4 trillion won ($58.5 billion), exceeding market expectations.The sharp sell-off suggested that investors had been looking for an even stronger earnings surprise, with profit-taking emerging as the dominant short-term market driver.The Kospi extended its losses as foreign investors ramped up selling pressure from the opening bell. As of 2:50 p.m., foreign investors had posted net sales of more than 3.75 trillion won, fueling the market's sharp decline.Although retail and institutional investors were net buyers, purchasing 3.43 trillion won and 23.9 billion won, respectively, their buying was not enough to offset the sharp sell-off.Samsung Electronics fell 6.92 percent to 296,000 won, while SK hynix slid 6.53 percent to 2.19 million won as of 2:50 p.m.The sell-off spread across other large-cap stocks. SK Square tumbled 10.77 percent to 1.334 million won, while Samsung Electro-Mechanics dropped 10.61 percent to 1.634 million won.