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MEXICO CITY — A strong new earthquake shook Mexico on Saturday, killing at least two people, toppling already damaged homes and a highway bridge, and causing new alarm in a country reeling from two even more powerful quakes that together have killed more than 400 people.

The U.S. Geological Survey said the new, magnitude 6.1 temblor was centered about 11 miles south-southeast of Matias Romero in the state of Oaxaca, which was the region most battered by a magnitude 8.1 quake on Sept. 7.

It was among thousands of aftershocks recorded in the wake of that earlier quake, which was the most powerful to hit Mexico in 32 years and killed at least 96 people.

The government of Oaxaca state reported that some homes collapsed. A woman died when a wall of her home fell on her in the town of Asuncion Ixtaltepec, and a man died after a wall fell on him in San Blas Atempa.

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Four people were injured in Juchitan and three in Tlacotepec, but none of their lives were in danger. Another person suffered a broken clavicle in the town of Xadani. Three hotels and two churches were damaged and a highway bridge collapsed. The Federal Police agency said the bridge already been closed due to damage after the Sept. 7 quake.

Bettina Cruz, a resident of Juchitan, Oaxaca, said by phone with her voice still shaking that the new quake felt "horrible."

"Homes that were still standing just fell down," Cruz said. "It's hard. We are all in the streets."

Rescue workers embrace each other deeply moved after a seismic alert sounded in Mexico City on Sept. 23, 2017, four days after the powerful quake that hit central Mexico. Ronaldo Schemidt / AFP - Getty Images

Cruz belongs to a social collective and said that when the shaking began, she was riding in a truck carrying supplies to victims of the earlier quake.

Nataniel Hernandez said by phone from Tonala, in the southern state of Chiapas, which was also hit hard by the earlier quake, that it was one of the strongest aftershocks he has felt.

"Since Sept. 7 it has not stopped shaking," Hernandez.

U.S. Geological Survey geophysicist Paul Caruso said the new temblor was an aftershock of the 8.1 quake, and after a jolt of that size even buildings left standing can be more vulnerable.

"So a smaller earthquake can cause the damaged buildings to fail," Caruso said.

"At the moment the greatest damage has been to the Ixtaltepec bridge, which should be rebuilt, and structures with previous damage that collapsed," President Enrique Pena Nieto tweeted. He said government workers were fanning out in Juchitan to provide help to anyone who needs it.

Jaime Hernandez, director of the Federal Electrical Commission, said the quake knocked out power to 327,000 homes and businesses in Oaxaca but service had been restored to 72 percent of customers within a few hours.

Buildings swayed in Mexico City, where nerves are still raw from Tuesday's magnitude 7.1 temblor that has killed at least 307 across the region. Many residents and visitors fled homes, hotels and businesses, some in tears.