A strong new earthquake shook Mexico on Saturday, killing at least one person, toppling already damaged homes and a highway bridge and causing new alarm in a country reeling from two quakes that together have killed over 400 people.
The U.S. Geological Survey said the new, magnitude 6.1 temblor was centred about 18 kilometres 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.
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."
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 said.
It was not immediately clear if there were any new injuries or damage from the latest tremor.
Alejandra Castellanos was on the second floor of a hotel in a central Mexico City neighbourhood and ran down the stairs and outside with her husband.
"I was frightened because I thought, not again!" she said.
At the site of an office that collapsed Tuesday, street signs swayed and rescuers briefly evacuated from atop the pile of rubble before returning to work.
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," Mexican 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 was restored to 72 per cent 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 305 across the region. Many residents and visitors fled homes, hotels and businesses, some in tears.
At the Xoco General Hospital, which is treating the largest number of quake victims, workers ordered visitors to evacuate when seismic alarms began to blare.
Getting used to it
That included Syntia Pereda, 43, who was reluctant to leave the bedside of her sleeping boyfriend. Jesus Gonzalez, 49, fell from a third-storey balcony of a building where he was working during Tuesday's quake and was awaiting surgery.
But she controlled her emotions, went outside and came back when the trembling was over.
"We are getting used to this," Pereda said. "Every so often we hear the alarm ... you say, well, it is God's will."
Mayor Miguel Angel Mancera said there were no reports of significant new damage in the capital, and rescue efforts related to Tuesday's quake were continuing. He reported that two people died of apparent heart attacks during the new temblor.
At the site of an office building that collapsed Tuesday and where an around-the-clock search for survivors was still ongoing, rescuers briefly evacuated from atop the pile of rubble after the morning quake before returning to work removing cement, tiles and other debris.
As rescue operations stretched into Day 5, residents throughout the capital have held out hope that dozens still missing might be found alive. More than half the dead — 167 — perished in the capital, while another 73 died in the state of Morelos, 45 in Puebla, 13 in Mexico State, six in Guerrero and one in Oaxaca.
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Along a 60-foot stretch of a bike lane in Mexico City, families huddled under tarps and donated blankets, awaiting word of loved ones trapped in the four-storey-high pile of rubble behind them.
Lidia Albarran, whose niece was buried in the collapse of an office building a block away, heard the alarm and worried that the latest quake could endanger those under the pile of rubble.
"You feel fear. Before, earthquakes did not make me afraid, but now ... thinking about all that could have happened in the building," Albarran said.