Mexico City (CNN) -- A strong 6.5-magnitude earthquake struck southern Mexico on Saturday night, about 100 miles south-southwest of the capital, the U.S. Geological Survey said. The quake, which hit at 7:47 p.m. local time, had an estimated depth of 40 miles, the USGS said. The agency earlier said it was 6.7 magnitude. There were no immediate reports of major damage in the capital, but several areas were without power, Mexico City Mayor Marcelo Ebrard wrote on his Twitter page. No injuries were reported in the quake, located in Guerrero state. Some startled residents in Mexico City ran out of their houses and into the streets. Loud sirens sounded. CNN's Jose Armigo contributed to this report.
NEW: Mexico City's mayor reports some blackouts, no major damage . The depth of the quake was some 40 miles, the U.S. Geological Survey says . There were no immediate reports of injuries .