At least 237 people were killed by the 7.1-magnitude quake that struck about 150 km (90 miles) southeast of Mexico City on Tuesday afternoon, 32 years after a 1985 quake killed thousands.
Rescue workers were able to communicate with the girl, identified only as Frida Sofia, who responded that there were two other students nearby but she could not tell if they were alive, according to broadcaster Televisa, whose cameras and reporters had special access to the scene.
Rescuers previously had seen a hand protruding from the debris, and she wiggled her fingers when asked if she was still alive, Televisa said.
The girl's full name was not made public, but her family waited in anguish nearby, knowing that the bodies of 21 school children and four adults were already recovered from the Enrique Rebsamen School.
They and other parents clung to hope after rescue teams reported a teacher and two students had sent text messages from within the rubble.
Rescuers moved slowly, erecting makeshift wooden scaffolding to prevent rubble from crumbling further and seeking a path to the child through the unstable ruins. As in rescue scenes throughout the central Valley of Mexico, officials ruled out using heavy equipment as long as there were signs of life below.
Some 14 hours after the effort began, rescue workers in hard hats made an urgent plea on camera for beams and chains to support parts of the school ruins that were collapsing.
"We have a lot of hope that some will still be rescued," said David Porras, one of scores of volunteers helping the search at the school for children aged 3 to 14.
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