Which exchange suffered the biggest one-day percentage fall during the 1987 global stock-market crash?

The Hong Kong Stock Exchange suffered the biggest one-day percentage fall during the 1987 global stock-market crash.

Hong Kong’s market fell 45.8 percent between October 19 and October 26, 1987, as the crash spread through international financial centers. Trading was suspended for four days during the turmoil. The extreme decline reflected both global selling pressure and the market’s particular vulnerability to rapidly changing investor confidence.

The U.S. market’s Black Monday on October 19 is more famous because the Dow Jones Industrial Average lost 22.6 percent that day. However, the Hong Kong percentage decline over the crash period was substantially larger. Markets in Australia, Britain, Canada, and Japan also fell sharply.

The episode demonstrated how closely connected major exchanges had become. Investors reacted across time zones, and selling in one market influenced sentiment in the next. The crash led regulators and exchanges to develop circuit breakers and other mechanisms designed to pause trading during extreme price movements.