A powerful 7.6-magnitude earthquake struck southwest Mexico Tuesday, causing residents in the capital several hundred miles away to rush out onto the streets but no immediate reports of serious damage.

The quake struck near the tourist resort of Acapulco, just after midday some 15 miles (25 kilometers) northeast of the town of Ometepec, the US Geological Survey said. Earlier it had estimated the magnitude at 7.9, before downgrading it to 7.6.

"There are no reports of serious damage by the quake," President Felipe Calderon wrote on his Twitter account.

Humberto Calvo, from Guerrero state civil protection services, said Acapulco was free of damage.

But he warned: "The problem could be in some areas between Guerrero and Oaxaca (states). We're checking."

The quake's epicenter was between the two southern states, both bordering the Pacific ocean.

The Pacific Tsunami Warning Center said a destructive, widespread tsunami had not been generated but warned of possible "local tsunami effects."

"The earthquake is located inland from the coast," it added.

In Mexico City, the quake swayed buildings, telephone and power lines were cut off and traffic lights stopped working as office workers rushed into the streets.

Mexico City Mayor Marcelo Ebrand reported no serious damage was visible during a helicopter survey.

The mayor's Twitter account said the water system and other "strategic services" were not experiencing problems.

It was one of the strongest quakes to shake Mexico City since 1985, when an 8.1 quake left between 6,000 and 30,000 dead, according officials and rescue organizations respectively.