Mexican President Enrique Pena Nieto has declared three days of national mourning following Thursday's powerful earthquake that has killed at least 61 people.

"The power of this earthquake was devastating, but we are certain that the power of unity, the power of solidarity and the power of shared responsibility will be greater," Pena Nieto said in a televised address on Friday.

The US Geological Survey (USGS) reported the magnitude of the earthquake that hit southern Mexico late on Thursday as 8.1, but the president described it as an 8.2-magnitude quake - "the largest registered in [Mexico] in at least the past 100 years".

READ MORE: These are the deadliest quakes of the past 100 years

He said it was bigger than the one in 1985 that killed more than 10,000 people in Mexico City.

On Friday, police, soldiers and emergency workers raced to rescue survivors from the rubble of houses, churches and schools that were split down the middle.

Pena Nieto said that 61 people were killed, including 45 who died in Oaxaca state, 12 in Chiapas and four in Tabasco. More than 200 people were injured across Mexico, officials said.

Al Jazeera's David Mercer, reporting from Mexico City, said that as "rescuers reach the coastal areas in southern Mexico, close to the Guatemalan border, the death toll is expected to continue to climb".

 

'A disaster zone'

The worst-hit city was Juchitan, on the narrow waist of Oaxaca known as the Isthmus, where 36 quake victims died.

About half of Juchitan's city hall collapsed in a pile of rubble and streets were littered with the debris of ruined houses.

On Friday, a crowd had formed outside the city 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 earthquake.

"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.

Hundreds of buildings have been completely destroyed [Pedro Pardo/AFP]

A police officer who had been working for days told AFP news agency that he could not remember an earthquake "this terrible".

"The whole city is a disaster zone right now. Lots of damages. 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 hospital also collapsed, Pena Nieto said after touring Juchitan and meeting with residents. The patients were relocated to other facilities.

The president said authorities were working to re-establish the supply of water and food and provide medical attention to those who need it. He vowed the government would help people rebuild and called for people to come together.

READ MORE: Powerful earthquake rattles Mexico

Elsewhere, the extent of destruction was still emerging. Hundreds of buildings collapsed or were damaged and power was cut at least briefly to more than 1.8 million people.

The Interior Department reported that 428 homes were destroyed and 1,700 were damaged in various cities and towns in Chiapas.

"Homes made of clay tiles and wood collapsed," said Nataniel Hernandez, a human rights worker living in Tonala, Chiapas, who warned that inclement weather threatened to bring more down.

"Right now, it is raining very hard in Tonala, and with the rains, it gets much more complicated because the homes were left very weak, with cracks," Hernandez told The Associated Press.

Hurricane Katia makes landfall

The tremor's epicentre was 123km southwest of the town of Pijijiapan, at a depth of 70km, according to USGS. 

Tsunami waves have been measured off Mexico's Pacific coast; the Pacific Tsunami Warning Center said waves of one metre above the tide level were measured off Salina Cruz. Officials, however, said there was no major damage from the sea.

The earthquake was also felt in much of El Salvador, as well as Guatemala, where at least four people were injured and several dozen homes damaged.

The earthquake struck as Mexicans were also bracing for Hurricane Katia, which made landfall on Friday night on Mexico's Gulf coast as a Category 1 storm. 

It is one of three active hurricanes currently in the Atlantic Ocean alongside Irma and Jose.

Katia landed with sustained winds of 75 mph (120 kph), according to the US National Hurricane Center.

"The arrival of Katia may be particularly dangerous for slopes affected by the earthquake. Avoid these areas," Pena Nieto tweeted on Friday.

Mexico sits atop five tectonic plates, making it prone to earthquakes, and has two long coastlines that are frequently battered by hurricanes.

Officials said that more than 200 people were injured in the earthquake [Pedro Pardo/AFP]

Source: Al Jazeera and news agencies