TEHRAN, Young Journalists Club (YJC) - Mexico's civil protection agency said it was the strongest earthquake to hit the capital since a devastating 1985 tremor that flattened swathes of Mexico City and killed thousands.
There were no immediate reports of major damage but windows were broken at the airport and power went out in several major neighborhoods of the capital. The cornice of a hotel collapsed in the southern tourist city of Oaxaca, a witness said.
People in the capital, one of the world's largest cities, ran out into the streets in pyjamas and alarms sounded after the quake struck just before midnight, a Reuters witness said.
Helicopters hovered overhead a few minutes later, apparently looking for damage to buildings in the city built on a spongy, drained lake bed.
In one central neighbourhood, dozens of people stood outside after the quake, some wrapped in blankets against the cool night air. Children were crying.
Liliana Villa, 35, was in her apartment when the earthquake struck and she fled to the street in her pyjamas. "It felt horrible, and I thought, 'this is going to fall'."
The epicenter was 123 km (76 miles) southwest of the town of Pijijiapan, at a revised depth of 43 miles. Widespread, hazardous tsunami waves were possible within three hours, the Pacific Tsunami Warning Centre said.
USGS reported several aftershocks, all greater than 5 magnitude.