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South of Mexico City, the Popocatepetl volcano sent a column of ash into the sky, capping a period of seismic activity including two powerful tremors this month that have killed more than 400 people and caused damages of up to $US8 billion ($NZ10.9 billion).
Mexico's capital was shattered by Tuesday's magnitude 7.1 quake that flattened dozens of buildings and killed at least 307 people. The government's response to the disaster is under close scrutiny ahead of a presidential election next year.
Although the latest quake was not as destructive, fear is running high among the population. Terrified residents crouched and prayed when the alarms went off and two women died of heart attacks as the ground shook, the city government said.
Concern that the quake could cause further collapses paralyzed rescue efforts at a housing complex in the Tlalpan neighborhood of Mexico City, frustrating first responders who earlier believed people were alive under the rubble.
By the evening, hard-hatted first responders were again digging for bodies or survivors. Elsewhere, the work barely skipped a beat when earthquake alarms twice rang out across the streets of the city.
The United States Geological Survey said the latest quake was relatively shallow with an epicenter near Juchitan, a tropical region of Oaxaca state hard hit by a massive 8.1 magnitude tremor that struck on September 7.
Three people died during Saturday's tremor in Oaxaca, including a man who was attacked by a swarm of wild bees, authorities said.
Mexico's seismological authorities said Saturday's quake was an aftershock of that tremor, which was the strongest to hit the country in 85 years and killed at least 98 people.
The Popocatepetl volcano, which is visible on a clear day to the approximately 20 million people that live in the Mexico City metropolitan region, spewed vapor and ash-filled gas after two small eruptions on Saturday.
Dozens of buildings were brought to the ground by Tuesday's earthquake and an army of trained rescuers and scores of volunteers have been frantically removing rubble in a day-and-night search for survivors.
Apartment buildings, offices, a school and a textile factory were among the structures flattened, leaving thousands homeless. The search had wound up at many sites by Saturday.
Officials said there could be some 30,000 badly damaged homes in the adjacent states of Morelos and Puebla. RMS, a risk modeling company, estimated economic losses of $US4 billion to $US8 billion.
After several days of searching, Mexican volunteers, professionals and soldiers backed by teams from countries as far away as Japan have saved 60 people from the rubble. But in the past 48 hours rescuers have found more corpses than survivors, and frustration was mounting.
The government has run a massive search and rescue operation involving thousands of soldiers and police, but in outlying areas of the city and surrounding villages, victims complained that help has been slow to arrive.
"Here we have no help, everything is the center (of the city)," said Justina Gonzalez (55), a shopkeeper in the Xochimilco district in the far south of the city whose two-bedroom house fell down on Tuesday. She now lives in a tent.
"We lost everything, we don't even have a way to cook," Gonzalez said, adding that neighbors were bringing her family food.
Caravans of volunteers were shuttling aid to isolated communities, with many from brigades organized at Mexico City universities. Others came from other parts of Mexico to help with the efforts.
Eleazar Hernandez (42), who sells candy in the rural state of Michoacan, said he helped clear rubble and then staffed a makeshift kitchen to feed people who lost their homes.
"It's the people, not the government, that are donating things," Hernandez said.
Tuesday's quake hit on the anniversary of the deadly 1985 tremor that by some estimates killed 10,000 people. A government response panned as lacking at the time severely damaged the credibility of the ruling Institutional Revolutionary Party.
Mexico is now better prepared to deal with the aftermath of earthquakes, helped by disaster planning, civic groups, a stringent building code and communication technology.