The quake rattled nerves of Mexicans already coping with an outbreak of the swine flu that has killed an estimated 149 people.
The combination of the higher death toll from the flu and the quake weakened the peso, which had lost nearly 5% from Friday's close to MXN13.975 per U.S. dollar.
The quake briefly interrupted a press conference in which Health Minister Jose Angel Cordova was giving an update on the flu emergency situation.
The U.S. Geological Survey said the epicenter was in the Pacific coast state of Guerrero, home to the resort of Acapulco, which lies roughly 360 kilometers from Mexico City.
The earthquake's depth made serious damage less likely, said Jim Dewey, a research geophysicist with USGS.
"Certainly strong shaking could be perceived, but it wouldn't likely cause extensive damage," Dewey said. "It was 25 miles deep, so that puts some distance between it and the surface of the ground."
Telephone service in parts of Mexico City was lost briefly. A spokesman for phone company Telefonos de Mexico (TMX) said lines were temporarily saturated with call volume, as usually happens after earthquakes, and that there was no reported damage to exchanges.
Mexicans, accustomed to earthquakes, largely shrugged off the tremor, worried more about the killer flu. "Ah, we're accustomed to earthquakes around here," said Leopoldo Garcia, a 70-year-old retiree walking around the city.
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