MEXICO CITY -- A powerful earthquake shook Mexico City and the country's Pacific coast late Tuesday, sending panicked residents spilling into capital streets and knocking out power to large swaths of the city.
The national seismological service said the 7.6-magnitude quake struck at 8:07 p.m. on the coast of Colima, a small state which includes the port city of Manzanillo, about 300 miles west of Mexico City.
The U.S. Geological Survey calculated the strength of the quake at magnitude 7.3.
"There are general reports of damage from the states of Colima, Michoacan and Jalisco," Survey spokesman Butch Kinerney said. "Because of the size of the earthquake and its shallow depth, USGA is expecting substantial damage."
Mexico's national civil defense chief Carmen Segura told local news media that there were no early reports of damage from Colima or the neighboring state of Jalisco.
But it was difficult to communicate with the area by telephone, partly due to overloaded lines.
In the Jalisco state capital of Guadalajara, Mexico's second-largest city, doctors treated dozens of people for panic, but there were no reports of physical injuries.
People rushed into the streets of Mexico City, many of them barefoot or wrapped in blankets against the chill.
Police cars drove slowly through the streets of Mexico City with sirens flashing, asking people over loudspeakers: "Is everything OK?"
Some earthquakes of magnitude 7 have caused massive damage, but the effect of a quake can be affected by many factors, including its depth and the sort of earth through which it moves away from the epicenter.
Mexico City is built atop a former lakebed which acts as a sort of loudspeaker that magnifies the sensation of quakes.