The worldwide market collapse that began in Hong Kong on 19 October 1987 is known as Black Monday.
Hong Kong’s Hang Seng Index fell 45.8% during the crash period, and the selling then spread westward through international markets. When New York trading ended, the Dow Jones Industrial Average had fallen 22.6%, its largest one-day percentage decline in history.
The crash was not confined to the United States. Australia, Canada, Britain, and many other markets recorded dramatic losses. The global sequence showed how increasingly connected financial markets had become through international investment and rapid communications.
Although the date was a Monday in New York, time-zone differences meant that markets in Asia had already experienced the shock before U.S. trading began. The same event is therefore described through different local dates in some historical accounts, but Black Monday is the standard name.