The temblor occurred 123 kilometre to the southeast of Salina Cruz, which is located on Mexico's southern Pacific coast in the state of Oaxaca, Efe news reported.
A quake with a 6.2 magnitude shook southern Mexico on Saturday and was felt in the capital, where seismic alarms sounded, residents ran into the streets and rescuers briefly stopped combing the rubble left by a bigger tremor earlier this week.
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.
The tremor was mild in Mexico City but thousands of residents, many wearing pyjamas, ran into the streets when seismic alarms sounded.
The remaining unidentified body was that of a woman pulled from a collapsed building in the chic neighborhood of Condesa.
Mexico's National Seismological Service says its own network has recorded thousands of aftershocks of the September 7.
There were no reports of new damage in the capital and rescue efforts were still the priority, Mexico City's Mayor Miguel Ángel Mancera said on Twitter (in Spanish).
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Martin Mendez, a locksmith, said he was working in a building when it collapsed.
Tuesday's quake, which toppled 39 buildings in the capital, was the worst natural disaster in three decades to hit Mexico City, following one in 1985 that killed 10,000 people.
Rescuers race against the clock early Saturday to reach possible survivors trapped inside an office building in the Roma Norte neighbourhood of Mexico City.
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 always believed I was going to get out alive", he said. More than half of the dead -157 - 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.
Along a 60-foot stretch of a bike lane in Mexico City's downtown, families huddled under tarps and donated blankets on September 22, awaiting word of loved ones trapped in the four-storey-high pile of rubble behind them.
"We had to hold on", he said.