The KOSPI plunged on March 31 as uncertainty surrounding the Iran situation remained, putting the 5,000 level at risk early in the session.

As of 9:38 a.m., the KOSPI was trading at 5,066.98, down 210.32 points, or 3.99 percent, from the previous session. The index opened at 5,143.75, down 133.55 points, or 2.53 percent, from the previous close, and extended its losses.

In the market, foreign investors were net sellers of 1.1133 trillion won and institutions net sold 213.0 billion won. Retail investors were net buyers of 1.2876 trillion won, appearing to try to limit the decline.

Top market-cap stocks fell across the board. SK Hynix was down 60,000 won, or 6.87 percent, at 813,000 won, while Samsung Electronics was trading at 168,300 won, down 8,000 won, or 4.54 percent.

SK Square fell 8.82 percent, Hanwha Aerospace slipped 5.28 percent, Hyundai Motor dropped 4.26 percent and Kia lost 4.42 percent. LG Energy Solution fell 3.05 percent, Doosan Enerbility slid 2.12 percent and Samsung Biologics dropped 1.05 percent.

The Kosdaq was down 34.89 points, or 3.15 percent, at 1,072.16.

The won was at 1,527.50 per dollar, up 10.00 won, or 0.66 percent, from the previous day.