Which 1987 crash saw Hong Kong’s Hang Seng Index fall 46% in five days?

The 1987 crash in which Hong Kong’s Hang Seng Index fell 46% in five days was Black Monday.

Black Monday refers to the worldwide stock-market crash that began on October 19, 1987. Hong Kong’s market was among the earliest and hardest hit, and the Hang Seng Index lost about 46% over five trading days. The panic then spread through time zones to Europe, the United States, and other markets.

In the United States, the Dow Jones Industrial Average suffered its record one-day percentage decline of 22.6% on October 19. Program trading, portfolio insurance, international market connections, and investor fear all played roles in the rapid selling, although no single explanation accounts for every market.

This question is distinct from the existing U.S.-focused question about the Dow’s October 19 decline: it asks for the global crash’s name using Hong Kong’s exceptional five-day fall as the identifying fact. “Black Tuesday” refers to a different historical market label.