Which index lost the greatest percentage in the 1987 global stock-market crash?

Hong Kong's Hang Seng Index lost the greatest percentage among major indexes in the 1987 global stock-market crash.

The crash began in Hong Kong before spreading through international markets. The Hang Seng fell by about 45.8% between October 19 and October 26, 1987, a much larger decline than the single-day losses recorded by several better-known Western indexes. The worldwide episode is often called Black Monday, after the sharp U.S. fall on October 19.

The 1987 crash had several proposed causes, including overvalued shares, trade tensions, rising interest rates, and computerized portfolio-insurance selling. The event also prompted exchanges to develop circuit breakers and other trading safeguards. It is a mistake to assume that the U.S. Dow suffered the largest percentage decline worldwide; its 22.6% one-day fall was historically dramatic but not the global maximum.