Rescue workers are scrambling through mounds of rubble in a harrowing search for dozens of children feared buried beneath a school hit by the Mexico Earthquake, which has killed at least 225 people.

Anxious parents could only watch as rescuers worked frantically Thursday morning (AEST) to free a young girl discovered alive beneath the partially collapsed building.

Twenty one children and two adults are believed to have died in the school collapse, but the toll could rise.

Television network Televisa broadcast the dramatic rescue attempt live after crews at the Enrique Rebasmen school in southern Mexico City reported seeing the girl move her hand before threading a hose through debris to get water to her.

The effort to rescue the girl is part of a search for dozens of victims feared buried beneath the school, one of hundreds of buildings destroyed Tuesday local time by the country’s deadliest earthquake in a generation.

“We have a lot of hope that some will still be rescued,” David Porras, one of scores of volunteers helping the search at the school for children aged 3 to 14.

“But we’re slow, like turtles,” he said.

Several children were earlier freed from the debris.

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The magnitude 7.1 quake, which killed at least 94 people in the capital alone, struck 32 years to the day after a 1985 Mexico earthquake that killed thousands. Mexico is also still reeling from a powerful tremor that killed nearly 100 people in the south of the country less than two weeks ago.

“The priority now is continue rescuing those who are still trapped and provide medical attention to the injured,” President Enrique Peña Nieto said.

As rescue efforts continued at the school, emergency crews, volunteers and bystanders toiled elsewhere using dogs, cameras and heat-seeking equipment to detect survivors.

Hundreds of neighbours and emergency workers spent the night pulling rubble from the ruins of the school with their bare hands under the glare of floodlights.

Three survivors were found around midnight local time as volunteer rescue teams known as “moles” crawled deep under the rubble.

Rescuers toiled through the night: Photo: Getty

By Wednesday morning, the workers said a teacher and two students had sent text messages from within the rubble. Parents clung to hope that their children were alive.

Overnight, volunteers with bullhorns shouted the names of rescued children so that tense family members could be reunited with them.

The Mexico earthquake toppled dozens of buildings, tore gas mains and sparked fires across the city and other towns in the country’s central region. Falling rubble and billboards crushed cars.

Devastating images from Mexico City. pic.twitter.com/RpF7sUq31s

— Jorge Guajardo (@jorge_guajardo) September 19, 2017

Even wealthier parts of the capital, including the Condesa and Roma neighbourhoods, were badly damaged as older buildings buckled.

Parts of colonial-era churches crumbled in the adjacent state of Puebla, where the US Geological Survey put the quake’s epicentre about 158km southwest of the capital.

Around the same time that the earth shook, Mexico’s Popocatepetl volcano, visible from the capital on a clear day, had a small eruption. On its slopes, a church in Atzitzihuacan collapsed during Mass, killing 15 people, Puebla governor Jose Antonio Gali said.

The quake is the deadliest in a generation. Photo: Getty

US President Donald Trump said in a tweet on Tuesday: “God bless the people of Mexico City. We are with you and will be there for you.” Trump and Mexican President Enrique Pena Nieto spoke at length on Wednesday, according to the White House.

Residents of Mexico City, home to about 20 million people, slept in the streets while authorities and volunteers distributed food and water at tented collection centres.

Other volunteers, soldiers and firefighters formed human chains and dug with hammers and picks to find dust-covered survivors and bodies in the remains of apartment buildings, schools and a factory.

With power out in much of the city overnight, the work was carried out with flashlights and generators.

– With agencies