The earthquake occurred at 10:29 am local time (11:29 am ET), with an epicenter 6.8 miles southwest of Santa María Zapotitlán in the state of Oaxaca, near El Coyul.
The earthquake could be felt up to Guatemala, Honduras and El Salvador. In the capital, Mexico City, approximately 190 miles north of El Coyul, tremors were heard and sirens were heard.
Waves of 0.68 meters (2.2 feet) were observed in Acapulco and 0.71 meters (2.3 feet) in Salina Cruz.
The Pacific Tsunami Warning Center said that dangerous tsunami waves are possible within 1,000 kilometers (621 miles) of the epicenter, even along the coasts of Mexico, Honduras, Guatemala and El Salvador.
Estimates modeled by the USGS suggest that localized casualties and damages are possible, but there are likely to be fewer than 100 deaths and less than $ 100 million in damages. However, the model only includes earthquake tremors, and no impact of possible tsunamis on the coast.
The USGS said that recent earthquakes in the area have caused secondary hazards such as tsunamis and landslides.
Civil protection in Oaxaca has not yet reported any significant damage.
Previous estimates put the magnitude of the earthquake at 7.7, but that has been revised to 7.4 (and additional revisions are possible).
Mexico is one of the most active seismic regions in the world and has a long history of devastating earthquakes. The country is located at the top of three large tectonic plates and its movement causes regular earthquakes and occasional volcanic eruptions.
Mexico City is particularly vulnerable to earthquakes because its very soft and moist soil amplifies shaking and is prone to liquefaction, in which dirt turns into a dense liquid when it is shaken enough.
This breaking story has been updated with additional reports.