The U.S. Geological Survey set the intensity of the first quake at 7.6 and said the epicenter was 11 miles underground and was felt strongly in Oaxaca. Mexico's National Seismological Survey said the tremblor had an epicenter southwest of Ometepec in Guerrero state.
Mexico City Mayor Marcelo Ebrard's Twitter account said the water system and other "strategic services" were not experiencing problems.
But frightened workers and residents poured into the streets of the capital just minutes after noon local time.
President Felipe Calderon said there were no immediate reports of damage through his Twitter account. Telephone service was down in the city and throughout the area where the quake was felt.
"I have problems with pressure, I felt I was going to faint," said Rosa Maria Lopez Velazquez, 62, outside a mall in Mexico City.
The quake was felt in southern Oaxaca state next to the epicenter in Guerrero.
"It was very strong, but we didn't see anything fall," said Irma Ortiz, who runs a guesthouse in Oaxaca. She said their telephones are down, and that the quake shook them side-to-side.
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