Police, soldiers and emergency workers raced to rescue survivors from the ruins of Mexico's most powerful earthquake in a century, which killed at least 61 people, as storm Katia menaced the country's eastern coast on Saturday with heavy rains.

In the southern region hit hardest by the quake, emergency workers looked for survivors — or bodies — in the rubble of houses, churches and schools that were torn apart in the 8.1-magnitude quake.

President Enrique Pena Nieto said that 45 people were killed in Oaxaca state, 12 in Chiapas and four in Tabasco. But the actual death toll could be over 80, according to figures reported by state officials.

Storm 'Katia' to bring heavy rains

Meanwhile, storm Katia made landfall in the east as a Category One hurricane and hours later was downgraded to a tropical storm with maximum sustained winds of 45 miles (70 kilometers) per hour.

The storm was bringing rains likely to cause "life-threatening flash floods and mudslides, especially in areas of mountainous terrain" the US National Hurricane Center said.

Katia was lashing the state of Veracruz, which borders the Gulf of Mexico, as well as parts of Hidalgo and Puebla. Forecasters were predicting the storm could unleash upwards of 25 inches (64 centimeters) of rain in some areas.

In Tecolutla, a coastal town of 8,000 residents, AFP journalists found felled trees and branches as families hunkered down to weather the storm.

The government warned that Katia could threaten about one million people and unleash dangerous floods.

Adding to the concerns, authorities warned another massive aftershock could follow within 24 hours of the first quake.

Juchitan, the hardest-hit city

Pena Nieto toured the hardest-hit city, Juchitan in Oaxaca, where at least 36 bodies were pulled from the ruins.

The city's eerily quiet streets were a maze of rubble, with roofs, cables, insulation and concrete chunks scattered everywhere.

A crowd had formed at Juchitan's partially collapsed town hall, a Spanish colonial building where two policemen were trapped in the rubble.

Rescuers managed to extract one and were still working to save the other 18 hours after the quake.

"God, let him come out alive!" said a woman watching as four cranes and a fleet of trucks removed what remained of the building's crumbled wing.

His blue uniform covered in dust, Vidal Vera, 29, was one of around 300 police officers digging through the rubble. He hadn't slept in more than 36 hours.

"I can't remember an earthquake this terrible," he told AFP.

"The whole city is a disaster zone right now. Lots of damage. Lots of deaths. I don't know how you can make sense of it. It's hard. My sister-in-law's husband died. His house fell on top of him."

A hotel mostly collapsed and many homes were badly damaged in the predominantly indigenous town of 100,000 people, which is tucked into the lush green southern mountains near the coast.

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.

"The priority in Juchitan is to restore water and food supplies and provide medical attention to those affected," Pena Nieto tweeted after visiting the devastated town.

The president described the quake as "the largest registered in our country in at least the past 100 years" — stronger even than a devastating 1985 earthquake that killed more than 10,000 people in Mexico City.

In Tabasco, two children were among the dead. One was crushed by a collapsing wall. Another, an infant on a respirator, died after the quake triggered a power outage.

Pope Francis, at an open air mass on a visit to Colombia, said he was praying "for those who have lost their lives and their families" in the disaster.

More than 200 people were injured across Mexico, officials said.