BEIJING -- A series of strong earthquakes struck China's western Qinghai province Wednesday, toppling houses, killing at least 67 people and burying many others in a mountainous rural area, officials and state media said. The U.S. Geological Survey reported on its Web site that a magnitude 6.9 temblor struck an area in southern Qinghai, near Tibet, on Wednesday morning and was followed by three quakes in the same area.