The KOSPI and KOSDAQ were hit by what the article called an “Iran shock” over fears of a full-scale war between the United States and Iran, posting their steepest declines since 2000. The two markets also saw circuit breakers triggered simultaneously for the first time in 1 year and 7 months, underscoring extreme fear-driven trading.

On Tuesday, the KOSPI closed at 5,093.54, down 698.37 points, or 12.06 percent, from the previous session. The fall exceeded the 12.02 percent drop seen during the Sept. 11 attacks in 2001, marking the biggest one-day plunge since 2000.

The index opened down 199.32 points, or 3.44 percent, at 5,592.59 and extended losses. It sank as far as 5,059.45 at one point, threatening to break below the 5,000 level.

Amid the rout, a sell-side program trading curb known as a sidecar was triggered on the KOSPI at 9:05 a.m. Level-one circuit breakers were then triggered on the KOSDAQ at 11:16 a.m. and on the KOSPI at 11:19 a.m., halting all trading for 20 minutes.

Simultaneous circuit breakers on the KOSPI and KOSDAQ were triggered for the first time in 1 year and 7 months since the so-called “Black Monday” in August 2024.

By investor type, retail investors and foreigners were net buyers of 72.9 billion won and 228.8 billion won, respectively, while institutions were net sellers of 579.4 billion won, driving the index plunge.

All of the top 10 stocks by market capitalisation fell sharply. Market bellwether Samsung Electronics closed at 172,200 won, down 22,900 won, or 11.74 percent, from the previous session, while SK Hynix ended down 9.58 percent at 849,000 won.

Hyundai Motor fell 15.80 percent and Kia dropped 14.04 percent. Other large-cap stocks also tumbled, including LG Energy Solution down 11.58 percent, SK Square down 12.74 percent, Samsung Biologics down 9.82 percent, Hanwha Aerospace down 7.61 percent and HD Hyundai Heavy Industries down 13.39 percent, reflecting the market shock.

The KOSDAQ also broke below the 1,000 level, closing at 978.44, down 159.26 points, or 14.00 percent, from the previous session.

The KOSDAQ’s percentage drop was also the biggest on record. The previous record fall was 11.71 percent on March 19, 2020.

A temporary halt on KOSPI program sell orders, known as a sidecar, was triggered for a second straight day. A sell-side sidecar on the KOSDAQ was triggered for the first time in four months.

In the Seoul foreign exchange market, the won was quoted at 1,475.00 per dollar as of 3:30 p.m., up 5.00 won, or 0.34 percent, from the previous session.