The U.S. Geological Survey said the quake was centered in a sparsely populated, mountainous area of Oaxaca near the southern Pacific coast.
Gilberto Lopez of the Oaxaca state civil defense department said his office is still assessing the situation and did not yet know if there were injuries or damage.
The U.S. Geological Survey said the quake hit at 2.22 a.m. local time (0722 GMT; 3:22 a.m. EDT). Its center was about 75 miles (120 kilometers) west-southwest of Oaxaca city, the state capital, and 220 miles (355 kilometers) south-southeast of Mexico City.
