The KOSPI plunged more than 8 percent, triggering a level 1 circuit breaker on the main board after a sell sidecar was activated. The circuit breaker has been triggered 7 times this year and 13 times ever.

The Korea Exchange said it activated the level 1 circuit breaker at 1:28 p.m. on July 13 after the KOSPI fell 604.74 points, or 8.08 percent, to 6,871.20 from the previous session's close of 7,475.94.

A level 1 circuit breaker is triggered when the KOSPI stays down 8 percent or more from the previous session for 1 minute.

Trading in listed stocks on the main board, excluding bonds, was halted for 20 minutes upon activation. The acceptance of new orders was also suspended, except for cancellation orders.

After 20 minutes, the trading halt is lifted across the board. Orders are then accepted for 10 minutes for a single-price auction before switching to continuous trading.

Trading in derivatives such as futures and spreads based on the main board as the underlying asset was also halted. Index-linked bonds were excluded from the trading halt.

Earlier, the exchange activated a sell sidecar at 10:34 a.m. on July 13, temporarily suspending the effectiveness of program sell orders on the main board.

Selling pressure, led by large semiconductor stocks, continued to grow, pushing the KOSPI's decline past 8 percent and triggering the circuit breaker.

The main board circuit breaker has been triggered 13 times in total through July 13 since it was first activated on April 17, 2000.

This year, it has been triggered 7 times in total, including on March 4, March 9, June 8, June 23, June 26 and July 7, as well as on July 13.

The exchange cited expanding geopolitical risks in the Middle East as a major reason for the activation on July 13.

A level 2 circuit breaker is triggered when, after a level 1 activation, the KOSPI falls 15 percent or more from the previous session and an additional 1 percent or more from the level 1 trigger level, and that condition lasts for 1 minute.

A level 3 is applied when, after a level 2 activation, the index falls 20 percent or more from the previous session and an additional 1 percent or more from the level 2 trigger level, and that condition lasts for 1 minute. If a level 3 is activated, trading ends for the day.