The Hang Seng Index lost more than 20% in a single day during the 1987 Black Monday crash.
On October 19, 1987, markets around the world plunged. Hong Kong’s Hang Seng Index fell 46% during the crash period, including a collapse of more than 20% in one session when trading resumed after a temporary closure.
The global sell-off followed a sharp rise in U.S. interest rates, concerns about valuation, currency tensions, and growing use of computerized trading and portfolio-insurance strategies. Market structures and trading rules also differed substantially between exchanges.
The New York Stock Exchange’s Dow Jones Industrial Average fell 22.6% on October 19, the largest one-day percentage decline in its history. That U.S. figure is often remembered most, but the crash was international and some markets recorded even larger percentage losses.