Adriana Fargo nervously bites her lip as she waits for news on the fate of her seven-year-old daughter, feared buried in the earthquake-hit remains of a Mexico City elementary and middle school.

At least 21 children died when a three story wing of the Enrique Rebsamen school collapsed after a 7.1 magnitude quake struck Mexico on Tuesday.

Thirty children are missing, and some could still be alive.

"No one can possibly imagine the pain I'm in right now," said Fargo, wrapped in a blanket as she sat with other anguished parents Wednesday in an improvised shelter near the school.

What is the girl’s name? Fargo's fists tighten and she stares at the ground, unable to pronounce her daughter's name. Her lips strain as she holds back what appears to be a mournful wail of pain.

After sunrise there was a glimmer of hope amid the torture of uncertainty: rescuers confirmed that they located a girl alive and trapped in the rubble.

There was a call for absolute silence as the rescuers slid a themal scanner down a narrow crack where they had made contact with the child.

"We are very, very close to people who could be alive. We're working with thermal cameras and canine units," said volunteer rescuer Pamela Diaz, a bread baker by profession.

"We keep moments of absolute silence to listen for survivors. They tend to cry out or bang on walls," she told AFP by telephone.

Another rescuer, 42 year-old Flor Gonzalez, gave a grim description her experience.

"Last night I counted five cadavers that were removed from the school," said Gonzalez, a dentist who spent the night volunteering at the school.

"I saw when they notified one of the parents . ... it was devastating," she said, as tears swelled in her eyes.

A third rescuer, speaking on condition of anonymity, earlier told AFP that there were signs of even more survivors -- possibly 20 children trapped inside a classroom with a teacher.

He said there also appeared to be nine lifeless bodies in the debris.

Up to now, 11 children and at least one teacher were pulled alive from the rubble.

However, rescuers also pulled out 26 lifeless bodies -- all but five of them children, said rescue coordinator Jose Luis Vergara.

President Enrique Pena Nieto, who rushed to the site late Tuesday, warned that the death toll could rise.

At least 217 people were reported killed by the earthquake.

- Picks, shovels and hands -

Fargo's husband joined the hundreds of soldiers, firefighters and rescuers clawing away at the debris since the quake struck.

Armed with picks, shovels and even their bare hands, the crew worked through the night in their desperate search for survivors.

"Silence, please!" a police officer barked through a megaphone. "Don't walk, don't breathe, we're trying to hear voices!" Any sign of life from under the rubble was welcome.

A stream of volunteers, many with lamps attached to their helmets, carried long wooden beams to prop up building sections that were in danger of collapsing.

Other volunteers formed a human chain to hand baskets of bottled water to the rescuers. The baskets then returned filled with debris.

Maria del Pilar Marti, a teacher who works at the Enrique Rebsamen school, said that many children stayed in the building when the quake hit.

"We had to take cover in our classrooms until the quake ended," she told Televisa news. "Then we were covered in a cloud of dust when part of the building totally collapsed."

Tuesday's earthquake struck as the country was recovering from an 8.2 magnitude quake that hit on September 7 in southern Mexico, killing around 100 people and destroying homes.

In the aftermath Mexican authorities said they had inspected the country's schools, and verified that the structures were quake resistant.

The earthquake also hit on the anniversary of a massive 1985 quake that killed more than 10,000 people, an event that still haunts a country that has seen its share of disasters.

- 'It's chaos' -

Power outages, intermittent cell phone coverage and roads closed due to debris complicate the rescue.

In front of the school, two people sat at a table with a computer at an informal control center, keeping track of the children and teachers who died, those who were rescued and those still missing.

"It's chaos ... there are children that escaped the school but were injured, and are alone in hospitals without their parents," one of the people keeping track of the victims told AFP, speaking on condition of anonymity.

"Meanwhile here at school there are desperate parents that can't find their children."

Source: AFP