The 1987 global stock-market crash was called Black Monday in Hong Kong because the Hang Seng Index plunged on October 19, 1987.
Black Monday began as a worldwide equity-market panic. Hong Kong’s market was among the first major exchanges to suffer a dramatic fall because of its time zone, and the shock spread westward through Asian, European, and North American markets. The Hang Seng Index ultimately fell 46 percent between October 19 and October 26.
The same date is especially associated with the United States, where the Dow Jones Industrial Average lost 22.6 percent on October 19. A common mix-up is to treat “Black Monday” as one country’s exclusive label; the term describes the global event, while different exchanges experienced different declines and trading conditions.