In Huatulco, a laid-back beach destination known for surfing and small protected coves, the earthquake knocked goods off shelves and some rubble from buildings.
Mari González of the Princess Mayev hotel in Huatulco said staff and guests were able to evacuate the building before the quake, but that 45 minutes after the initial quake they were still outside as strong aftershocks continued.
"It was strong, very strong," she said.
González said there was some visible broken glass and mirrors, but no major damage. The staff was waiting for the aftershocks to dissipate before fully evaluating the property.
Local news media reported damage to some buildings in the state capital, Oaxaca city. State officials said they were looking for damage.
The USGS estimated that some 2 million people felt strong or moderate shaking and another 49 million felt weak or light shaking. Guatemala's national disaster agency issued a tsunami alert for its southern Pacific coast forecasting the arrival of waves up to a meter high. It advised people to move away from the sea.
The US National Oceanic and Atmospheric Administration forecast a tsunami threat with waves three to 10 feet above tide levels along parts of the coasts of Mexico.
Smaller waves were expected through Central America, Peru and Ecuador.
- AP