HONG KONG — A series of earthquakes in Gansu Province in northwestern China set off landslides and building collapses in an impoverished mountainous region Monday, killing at least 89 people, injuring more than 600, damaging tens of thousands of homes and prompting President Xi Jinping to order “all-out rescue efforts.”

The Gansu Provincial Seismological Bureau estimated the magnitude of the main earthquake at 6.6. The United States Geological Survey listed three fairly strong earthquakes in Gansu Province on Monday morning but none quite that powerful, with preliminary magnitudes of 5.9, 5.6 and 4.7.

Image Credit... The New York Times

The quakes took place along the border between Minxian County and Zhangxian County, both in the south of Gansu Province. Most of the deaths and injuries occurred in Minxian County, and all of the missing were there.