The KOSPI added 874 points in the first hour of Friday trading, and the only curb the exchange has for a rise ran for five minutes

The index gained more in an hour than it has ever gained in a day.

Seoul's benchmark opened on Friday at 5,657.79, up 64.23 points and 1.15 percent on Thursday's close, and then went vertical. At 9:58 a.m. the KOSPI stood at 6,467.94, a gain of 874.38 points or 15.63 percent, according to Oh Kuemin at The Asia Business Daily. Two minutes later the same paper put it at 6,490.53 and 16.04 percent. By 10:20 a.m. Choi Ji-won at The Korea Herald had it 16.8 percent higher at around 6,530, minutes after an intraday high of 6,548.64. The Asia Business Daily reports that the previous record single-day gain was 11.95 percent, on 30 October 2008, and that this was the first time the index had risen by more than 800 points in a day.

Trading in Seoul was still open when this was published.

The curb that fired

Six minutes after the opening bell, the Korea Exchange activated a buy-side sidecar and program trading bids on KOSPI-listed shares were suspended for five minutes. At the moment it triggered, the KOSPI 200 futures index had risen 129.90 points, or 14.97 percent, to 997.50, per The Asia Business Daily. A sidecar fired on the KOSDAQ one second later. Yoon So-yeon at the Korea JoongAng Daily and a Yonhap report carried by The Korea Times both put the KOSPI activation at 9:06 a.m. and source it to the exchange.

The exchange's own guide to trading in the Korean market sets out both thresholds, and they are not the same. A KOSPI sidecar activates when the KOSPI 200 futures price moves 5 percent or more from its base price and the move holds for one minute. A KOSDAQ sidecar needs the KOSDAQ 150 futures to move 6 percent and the KOSDAQ 150 index itself to move 3 percent in the same direction. That difference is why the two did not fire in the same second.

The guide also states that the sidecar is activated once a day, in either direction, from 09:05. Friday's was spent at 9:06 a.m.

What rose, and what did not

Electrical and electronics, the sector holding the chipmakers, rose 24.66 percent. Medical and precision instruments rose 14.55 percent, machinery and equipment 11.28 percent, distribution 11.08 percent and construction 9.53 percent. Food, beverages and tobacco fell 3.44 percent and pharmaceuticals fell 2.28 percent. SK Innovation was down 7.2 percent, Samsung Biologics 3.2 percent, KT&G 3 percent and Meritz Financial Group 2.8 percent, on a morning when the index they sit in was up more than 15.

Samsung Electronics rose as much as 26.3 percent, to 261,500 won, and SK hynix as much as 29.7 percent, to 1,715,000 won, on The Korea Herald's 10:20 a.m. reading. SK Square and Samsung Electro-Mechanics were both at the 30 percent daily price limit.

Foreign investors had bought a net 5.1693 trillion won of KOSPI shares by 9:58 a.m., The Asia Business Daily reported. Individuals sold a net 4.8464 trillion won over the same span and institutions a net 238.8 billion won. The Korea Herald put the foreign figure at 4 trillion won inside the first 20 minutes. The won went the other way, at 1,434.9 to the dollar at 10:20 a.m. against an opening 1,425.1.

The cause the reporting names

Both papers attribute the move to Thursday's close in New York, where the S&P 500 rose 1.66 percent, the Nasdaq 2.78 percent and the Dow Jones Industrial Average 1.19 percent, and the Philadelphia semiconductor index rose 8.19 percent. Microsoft rose 15.51 percent after its results, which this publication covered on Wednesday evening. Sangyoung Seo of Mirae Asset Securities told The Asia Business Daily that American chip stocks, which had fallen for five consecutive sessions, rebounded on results from Samsung Electronics and Microsoft together with options flows.

That is the explanation the market participants quoted are offering. This brief does not supply one of its own, and a first hour is not a session.

The week this reverses

Thursday's close, from which every percentage above is measured, was 5,593.56. It was the third consecutive fall. Sidecars have now been activated 42 times on the KOSPI this year, the highest annual total on record, the Korea JoongAng Daily reported on 28 July citing the Korea Exchange, against a previous record of 26 during the 2008 financial crisis. That article carries no individual byline and is filed to the paper's news team.

The Korea Exchange publishes no English notice of individual sidecar activations, so there is no primary document of Friday morning's. The document linked above is the exchange's statement of the rules, not a record of the event.