MEXICO CITY — A strong earthquake on the Pacific coast of Mexico shook the capital on Thursday, sending frightened office workers streaming into the streets away from high-rise buildings. The 6.4-magnitude temblor in southern Guerrero state had an epicenter about 9 miles (15 kilometers) north of Tecpan de Galeana and about 171 miles (277 kilometers) southwest of Mexico City, according to the U.S. Geological Survey. There were no immediate reports of injuries or damage. The quake had a depth of 23 kilometers. There was only mild shaking in the resort city of Acapulco, according to an Associated Press reporter there. The USGS downgraded the magnitude from 6.8. Carmen Lopez, an elegantly dressed businesswoman from Michoacan, was leaving a downtown Mexico City office building when the ground began to sway. She dashed across the street to a leafy median as light poles swayed violently above her. More