The Chi-Chi earthquake (also known as 921 earthquake) occurred on September 21, 1999 in central Taiwan at 1:47 am local time (September 20 17:47 GMT) and measured 7.6 on the Richter scale. Its epicenter was at 23.87° N latitude, 120.75° E longitude, which is in the Ji-Ji Township (Chi-Chi by Wade-Giles romanization) in the Nantou County, about 12.5 km west of the Sun Moon Lake. The depth was 7.0 km.

The earthquake caused extensive damage. Over 2400 people were killed. Numerous roads and bridges were damaged.