The Korea Exchange (KRX) after-market recorded average daily turnover of more than 1 trillion won within a week of its launch.

KRX said on Sunday that average daily volume in the after-market was 54.85 million shares and turnover was 1.1 trillion won from Sept. 14 to 18. Turnover was about 4.6 percent of the regular session over the same period.

By investor type, retail accounted for most of traded value at 90.4 percent. Foreign investors made up 6.7 percent and institutions 2.6 percent.

Of 2,763 listed issues eligible for trading, 2,379 saw executions, representing 86.1 percent of the total. Issues with notably low liquidity or requiring market management were excluded from after-market trading.

KRX applies the same volatility interruption (VI) rules in the after-market as in the regular session and operates a market-maker system.

The number of VI triggers fell to 553 on Sept. 18 from 1,112 on the first day of trading on Sept. 14. After-market volume on Sept. 18 was about 6.1 percent of the KRX regular session, but the number of VI triggers slightly exceeded the regular market's daily average of 494 this year.

The exchange explained that a high number of VI triggers alone does not make it difficult to view after-market volatility as high. It said VI blocks executions at abnormal prices and helps find an appropriate price through single-price trading, serving to ease price swings.

High-low volatility, which indicates the gap between the intraday high and low, was lower in the after-market than in the regular session. Average KOSPI high-low volatility from Sept. 14 to 18 was 3.8 percent in the regular session and 2.1 percent in the after-market. KOSDAQ showed 5.4 percent in the regular session and 3.5 percent in the after-market.

It will also strengthen monitoring for unfair trading as trading hours expand. The KRX Market Surveillance Commission will extend the operating hours for preventive measures against unfair trading and activate a nighttime monitoring system that integrates analysis of trading records from the regular session and the after-market.

It plans to operate an 'after-market special surveillance TF' through year-end. The task force will consist of 9 members, with 3 each for surveillance, prevention and short selling, and will be dedicated to monitoring after-market trading. The operating period can be extended depending on market conditions.

A KRX official said, "Considering market concerns over unfair trading in the early stage of introducing the after-market, we plan to operate a special surveillance system and respond strictly to unfair trading practices."