A magnitude-6.4 earthquake struck Afghanistan at a depth of 20 kilometers on Monday, according to the China Earthquake Networks Center.

The U.S. Geological Survey (USGS) measured the quake at magnitude 6.3, saying it struck near Mazar-i-Sharif, one of northern Afghanistan's largest cities.

The USGS issued an orange alert through its PAGER system, an automated tool that provides information on earthquake impacts, indicating that "significant casualties are likely and the disaster is potentially widespread."

(With input from Reuters)