Authorities say it was the strongest tremor to hit the country in a century.
Nieto said 45 deaths had been reported in Oaxaca, 12 in Chiapas and four in Tabasco. Tens of thousands of emergency packs, as well as 100 extra police officers and rescue dogs were sent to Juchitán, in Oaxaca, said to be the worst affected town.
The 8.2-magnitude natural disaster, the strongest ever hit the region in last 100 years, caused at least 61 deaths and injuries to 200 people in Mexican States including Tabasco, Oaxaca and Chiapas.
The 8.2-magnitude quake was felt by about 50 million people across the country.
President Enrique Pena Nieto described the 8.2 magnitude quake as "the largest registered in our country in at least the past 100 years" - stronger even than a devastating 1985 natural disaster that killed more than 10,000 people in Mexico City.
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Quake lights have been reported around the world for decades - with some claiming it's a natural phenomenon, and others claiming it's due to structural damage. It had a depth of 35 kilometers (22 miles). In September 1985, a magnitude 8.0 quake killed an estimated 9,500 people in and around Mexico City.
A tsunami was confirmed in Mexico, with the largest wave at 0.7 metres (2.3 feet). The town of Juchitán, in Oaxaca, was the wort-hit towns, there were reportedly 17 deaths. Earlier, the governor of Tabasco, Arturo Nunez, said two children had died in his state.
Officials warned the toll could continue to rise in the three hard-hit southern states. It also triggered a tsunami warning and the evacuation of thousands of people in coastal communities in Chiapas. It said the threat was still being evaluated for Hawaii, Guam and other Pacific islands. "Widespread destruction has been caused by the quake and about 1.85 million affected people are living under harsh conditions with no electricity and shortage of water", President Nieto said.
He said that there have been 62 aftershocks.