ACAPULCO, Mexico (AP) — A strong earthquake shook the southern Pacific coast of Mexico and several states, including the capital on Thursday, sending frightened people into unseasonal torrential rains that were also bearing down on the coast.

The 6.4-magnitude quake in southern Guerrero state had an epicenter about 9 miles (15 kilometers) north of Tecpan de Galeana, according to the U.S. Geological Survey, and was felt about 171 miles (277 kilometers) miles away in Mexico City, where office workers streamed into the streets away from high-rise buildings.

There were no immediate reports of injuries or major damage.

Tecpan, near the epicenter, shook ferociously, causing a “wave of panic” and some roofs to cave in, said Mayor Crisoforo Otero Heredia. But there were no injuries.

In Chilpancingo, the capital of Guerrero state, a wall collapsed and in Acapulco civil protection crews had found nothing so far except scared citizens who were forced to take refuge in the heavy rain that was hitting the region.

In Mexico City, elegantly dressed businesswoman Carmen Lopez was leaving a downtown office building when the ground began to shake. She dashed across the street to a leafy median as light poles swayed violently above her.

“That was just too scary,” said Lopez, as she quickly started dialing her cellphone to alert friends and family.

Behind her, thousands of people poured out from neighboring office buildings, following pre-planned evacuation routes to areas considered safe from any potential of falling glass.

The quake had a depth of 15 miles (23 kilometers). The USGS downgraded the magnitude from 6.8.

A 7.2-magnitude quake with an epicenter about 40 miles (66 kilometers) from Thursday’s quake shook central and southern Mexico on April 18.

That quake occurred along a section of the Pacific Coast known as the Guerrero Seismic Gap, a 125-mile (200-kilometer) section where tectonic plates meet and have been locked, meaning huge amounts of energy are being stored up with potentially devastating effects.

In 1911, a magnitude-7.6 temblor struck along the section, according to the USGS.

The USGS says the Guerrero Gap has the potential to produce a quake as strong as magnitude 8.4, potentially much more powerful than the magnitude-8.1 quake that killed 9,500 people and devastated large sections of Mexico City in 1985. The 1985 quake was centered 250 miles (400 kilometers) from the capital on the Pacific Coast.

Mexico City is vulnerable to distant earthquakes because much of it sits atop the muddy sediments of drained lake beds. They jiggle like jelly when the quake waves hit.

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Associated Press writer Mark Stevenson contributed to this report from Mexico City.

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