A 6.5-magnitude earthquake shook western Mexico Wednesday, the US Geological Survey said, with no immediate casualties reported as workers rushed onto the streets far away in Mexico City.

The temblor struck at 2255 GMT, with the epicenter located around 42 miles (69 kilometers) from the Pacific port of Lazaro Cardenas, in Michoacan state, the USGS reported.

The USGS initially put the quake at a magnitude of 7.0, but later revised down the figure.

Mexico's seismological service reported no immediate victims while the mayor of Mexico City, where power lines swayed and buildings shook more than 200 miles from the epicenter, said an initial survey showed no "major damage."

The international airport and communication networks were operating, Marcelo Ebrard wrote on his Twitter account, though cell phone networks were blocked as usually occurs after quakes here.

The head of civil protection in Michoacan state, Jorge Romero, told AFP there was no immediate damage but said authorities were still seeking updates from remote areas.

The quake followed a series of recent tremors in the region.

A powerful 7.4-magnitude earthquake struck southwest Mexico on March 20, killing two people, injuring 13 others and damaging thousands of homes.

Several hundred aftershocks have rocked south, western and central Mexico since then, including a 6.3-magnitude quake on April 2.

People in Mexico's crowded capital -- with more than 20 million in the metro area -- are all too familiar with seismic activity and used to evacuation drills.

The city government recently introduced an app for BlackBerry cellphones to give early earthquake warnings as well as plans to install public speakers to broadcast earthquake alarms.