The quake occurred at a depth of 12.4 miles, and was centered about 100 miles west-southwest of Oaxaca in Oaxaca state and about 200 miles south-southeast of Mexico City, the U.S. Geological Survey said. There were seven aftershocks of at least 5-magnitude over the next several hours, the USGS said.
CNN reported Guerrero state Gov. Angel Aguirre said at least 500 homes in the state were damaged, though there were no immediate reports of serious injuries or deaths. There were unconfirmed reports of many more homes destroyed, the U.S. news network said.
"There are many cracked ceilings, many houses that collapsed," Francisca Villalva Davila, the comptroller of Ometepec, a town in Guerrero, told CNN en Espanol.
Mexican President Felipe Calderon said while the initial reports were of minor property damage, there was "much fear, much panic," CNN said.
Government helicopters were deployed to survey the damage from the air and officials were getting shelters ready for displaced residents. Calderon said the country's healthcare facilities were intact and "all of the power generation facilities are unaffected and functioning."
Workers at two hotels in Oaxaca said they felt the buildings move.
"Yes, we felt the shaking for 15 to 20 seconds, but no damage," said a woman who works at the front desk of the Hotel Marina.
The temblor was felt in Mexico City and as far away as Guadalajara.
Mexico City Mayor Marcelo Ebrard said a pedestrian bridge fell on a minibus during the quake, there were no injuries.