An earthquake with a preliminary magnitude of 7.8 struck western China on Monday, the US Geological Survey reported. The quake struck 92 kilometers northwest of the Sichhuan provincial capital of Chengdu at 0628 GMT, the survey said on its Web site. It said the quake was centered 29 kilometers below the surface. In the Chinese capital Beijing, about 1,500 kilometers buildings swayed for more than two minutes but there were no immediate reports of damage or injuries. Calls to emergency response numbers in Chengdu, a city of about 10 million people, rang constantly busy on Monday.