A 5.6 magnitude earthquake hit southern Mexico this afternoon.
Buildings far away in the capital, Mexico City, were shaken but there were no immediate reports of deaths or damage.
Hundreds of people evacuated buildings in the capital, many of them wearing surgical face masks due to the swine flu outbreak.
The quake's epicentre was about 240km from Mexico City in the southern state of Guerrero, home to the well-known Pacific coast resort of Acapulco.
The USGS revised the quake's magnitude down to 5.6 from 6.0 initially, adding that the quake was 40km deep.
Quakes of magnitude 5.6 are classified as moderate, capable of causing considerable damage.
