The U.S. Geological Survey said it was centered northwest of the Pacific resort of Acapulco, where many Mexicans are vacationing for the Easter holiday. The quake was felt strongly in the resort city.
''There is a crisis of panic,'' said Alicia Dominguez, who answered the phone at the civil protection office. ''It's mainly the tourists who are shaken.''
Civil protection officials were patrolling the city to check for damage and casualties.
The quake struck 170 miles (273 kilometers) southwest of Mexico City, which shook for at least 30 seconds as people were enjoying a day off.
People fled high rises and took to the streets, where some were seen in bathrobes and pajamas talking to relatives on their cellphones.
''I started to hear the walls creak and I said, `Let's go,'" said Rodolfo Duarte, 32, who fled his third-floor apartment.
''This is really strong,'' said Gabriel Alejandro Hernandez Chavez, 45, an apartment building guard in central Mexico City. ''And I'm accustomed to earthquakes.''
The USGS initially calculated the quake's magnitude at 7.5, but later downgraded it to 7.2. It said the quake was , the quake's center was 15 miles (24 kilometers) deep.
Federal civil protection officials said the quake was felt across at least a half-dozen states.
''There are some broken windows, but so far we have no dead or injured,'' said Ricardo de la Cruz, director general of the Civil Protection Agency.
Mexico City is vulnerable even to distant earthquakes because much of it sits atop the muddy sediments of drained lake beds that quiver as quake waves hit.
The magnitude-8.1 quake in 1985 that killed at least 6,000 people and destroyed many buildings in Mexico City was centered 250 miles (400 kilometers) away on the Pacific Coast.