The epicentre of the quake was off the coast of Chiapas, a state in southern Mexico, but the rumblings rocked the Mexican capital more than 600 miles away, causing electricity failures, and reports of sporadic damage.
Mexico President Enrique Peña Nieto announced Friday that the quake killed 45 people in Oaxaca state, 12 in Chiapas and 4 in Tabasco.
In Veracruz, tourists abandoned coastal hotels as winds and rains picked up ahead of Hurricane Katia's expected landfall.
The Hurricane Center said Katia could still produce 3-6 inches of additional rain in a region with a history of mudslides and flooding.
He said the possible death occurred in San Marcos state near the border with Mexico.
The government warned that Katia could threaten about one million people and unleash unsafe floods.
The worst-hit city was Juchitan, on the narrow waist of Oaxaca known as the Isthmus, where 36 quake victims died.
The city's eerily quiet streets were a maze of rubble, with roofs, cables, insulation and concrete chunks scattered everywhere.
He told Radio Formula that rescuers were searching for a policeman thought to be buried under the rubble of a collapsed building in Juchitan, where the city hall was badly damaged, along with at least 7,000 homes.
The US Tsunami Warning System said hazardous tsunami waves were possible on the Pacific coasts of Guatemala, El Salvador, Costa Rica, Nicaragua, Panama and Honduras within three hours.
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His blue uniform covered in dust, Mr Vidal Vera, 29, was one of around 300 police officers digging through the rubble.
"It's unusual, but it's not unheard of", said seismologist Susan Hough of the USGS, describing how stresses on the seafloor can produce big earthquakes. "At first I laughed, but when the lights went out I didn't know what to do".
Singapore Prime Minister Lee Hsien Loong yesterday expressed "deepest condolences" to Mr Pena Nieto in a letter. The epicentre was in the Pacific Ocean, some 600 miles (1,000 KMs) southeast of the capital and 74 miles (120 KMs) off the coast, CNN reported. "His house fell on top of him".
The governor said tens of thousands of ration packs, blankets and cleaning kits were arriving, along with 100 federal police reinforcements with rescue dogs to search for people in the wreckage.
Three people died in Chiapas and two in the town of Tabasco.
The president said authorities were working to re-establish the supply of water and food and provide medical attention to those who need it. Another, an infant on a respirator, died after the quake triggered a power outage. Authorities say two people were killed by a landslide in Veracruz state.
A monster 8.2 magnitude natural disaster brought an unusual phenomenon that lit up the sky as it hit Mexico's coast, killing at least 60 people.
Power was cut at least briefly to more than 1.8 million people due to the quake, and authorities closed schools in at least 11 states to check them for safety.
Many were asleep when the quake struck. Tsunami warnings were issued as far away as New Zealand and Vanuatu.
Even at that distance, Mexico City is vulnerable because it sits on an ancient lake bed and the relatively loose soil makes it prone to severe shaking.