South Korea's KOSPI plunged more than 4 percent in early trade, breaking below the 6,100 level. Weakness in U.S. semiconductor stocks carried into the local market, while foreign investors turned net sellers. Major chip stocks, including Samsung Electronics and SK Hynix, were down about 5 percent.

As of 9:07 a.m. on Oct. 13, the KOSPI was down 270.34 points, or 4.23 percent, at 6,113.90 from the previous session. The index opened down 198.16 points, or 3.10 percent, at 6,186.08. Losses widened immediately and it briefly fell below 6,100.

Foreign investors were net sellers of 343.1 billion won, weighing on the index. Retail investors were net buyers of 133.0 billion won and institutions bought a net 201.3 billion won.

Large-cap stocks by market value also fell broadly. Samsung Electronics was trading down 4.59 percent at 239,000 won, while SK Hynix was down 5.05 percent at 1,524,000 won.

SK Square was down 6.91 percent, Samsung Electro-Mechanics fell 5.85 percent and LG Energy Solution lost 4.65 percent. Hyundai Motor slid 4.69 percent, KB Financial fell 2.58 percent, Samsung Biologics dropped 2.83 percent and Samsung Life slipped 4.30 percent. Most top market-cap stocks were lower.

The KOSDAQ was down 31.91 points, or 3.76 percent, at 817.28 at the same time.

The won-dollar exchange rate was 1,336.90 won per dollar, up 0.90 won from the previous session.

Weakness in the local stock market is being driven by a fall in U.S. semiconductor shares a day earlier. In U.S. trading on Oct. 12 (local time), the Dow Jones index rose 0.4 percent, but the S&P 500 fell 0.1 percent and the Nasdaq index dropped 0.4 percent. The Philadelphia Semiconductor Index fell 2.7 percent.

Chinese memory maker CXMT disclosed plans to launch next-generation DDR5 for servers, raising concerns over increased supply and intensified competition, which weighed on semiconductor investor sentiment. Micron fell 3.9 percent and SanDisk dropped 6.0 percent.

The local market has been sliding for 4 consecutive sessions through the previous trading day, with the KOSPI down a cumulative 8.9 percent.

Han Ji-young (한지영), a researcher at Kiwoom Securities, said the fallout from weakness in U.S. semiconductor shares triggered by China's CXMT would drive volatility early in the session. She said she expects the market to try to rebound during the day, supported by easing momentum in the rise of U.S. 10-year yields and inflows of technical and bargain-hunting buying after a recent string of sharp declines.