The KOSPI jumped more than 4 percent early on May 27 and briefly topped the 8,400 mark. Chip heavyweights such as Samsung Electronics and SK Hynix rose, and a buy sidecar was triggered on the main board.

As of 9:08 a.m., the KOSPI was up 339.88 points, or 4.22 percent, at 8,387.39. The index opened up 194.61 points, or 2.42 percent, at 8,242.12 and climbed to as high as 8,450.26 early in the session.

The Korea Exchange activated a buy sidecar at 9:06:02 a.m., temporarily halting the effectiveness of program buy orders on the main board after a sharp rise in KOSPI 200 futures. It was the first activation of a buy sidecar on the main board in 4 sessions.

By investor type, foreign investors were net buyers of 160.0 billion won. Individuals and institutions were net sellers of 37.2 billion won and 96.4 billion won, respectively. Foreign buying was supporting the index rise early in the session.

Most of the top market-cap stocks were higher, led by chipmakers. Samsung Electronics was up 6.86 percent at 319,500 won and SK Hynix was surging 9.41 percent at 2,245,000 won.

SK Square was up 9.10 percent, Samsung Electro-Mechanics rose 5.66 percent, Samsung Life gained 3.88 percent and Doosan Enerbility added 0.18 percent.

Hyundai Motor was down 1.60 percent, LG Energy Solution fell 0.38 percent and HD Hyundai Heavy Industries was down 0.27 percent.

The early strength was largely driven by a sharp jump in large-cap semiconductor shares. Samsung Electronics and SK Hynix posted steep gains from the start of trading, leading the KOSPI higher.

After settling above the 8,000 level for the first time ever based on the previous session's close, the index's upward momentum has continued, including a move beyond the 8,300 level on the day.

The Kosdaq was down 15.00 points, or 1.28 percent, at 1,157.52 at the same time. While the KOSPI surged on gains in large-cap chipmakers, the Kosdaq was weaker early in a mixed market.

In the Seoul foreign exchange market, the won was at 1,505.80 per dollar, up 1.70 won.