Which market suffered the biggest one-day percentage loss on Black Monday in 1987?

The Hong Kong Stock Exchange suffered the biggest one-day percentage loss during the global Black Monday crash of 1987.

On October 19, 1987, Hong Kong’s Hang Seng Index fell 46.2%, a decline far larger in percentage terms than the 22.6% fall in the Dow Jones Industrial Average. The Hong Kong market had already begun weakening before the dramatic U.S. session, illustrating how international markets could transmit fear across time zones.

The crash then moved through other major financial centers. London’s FTSE 100 recorded a historic fall, while markets in Australia, Canada, and Japan also declined sharply. Trading systems, portfolio-insurance programs, and synchronized investor reactions amplified the movement.

The event is called Black Monday because October 19 was the key date in the United States and several other markets. In Hong Kong, however, the extraordinary percentage fall is an important part of the crash’s global history and is often overlooked in accounts focused only on Wall Street.