At least 25 people were killed when the 7.1 Magnitude earthquake brought part of a school in the Mexican capital tumbling down onto students and teachers on Tuesday. At least 21 of them were children.

An entire wing of the Enrique Rébsamen school in southern Mexico City -- a wing where elementary school-aged children were in class at the time -- collapsed.

With dust still hanging in the air, people on the streets outside rushed to try and find anyone trapped under the ruins of the heavy concrete structure.

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A video posted online early Wednesday morning by Univision shows a frantic man warning people to get away from the heavily damaged building because he can smell gas in the air before he comes to the aid of another who heard children crying from inside the debris.

The unidentified man who recorded the video rushes over and starts shouting for anyone available to come help.

"Come! There are kids here, come help!" he screams repeatedly. Moments later he and several other men look for the best way to get the children out, first by trying to pry a massive slab of concrete away from the main structure to open a wider hole.

The man with the camera decides it looks too risky to move the slab, as it could be supporting the rest of the rubble hanging over the kids' heads. A narrow gap in the rubble is the only way out.

Within a minute, a young girl is pulled crying and covered in dust from out of the debris and is handed to other helpers on the scene. Then the man recording the incident pulls a boy out, also sobbing, and hands him to another rescuer, trying to calm him down the whole time; "don't cry my boy, don't cry."

Rescue workers remove a dead body after searching through rubble in a floodlit search for students at Enrique Rebsamen school in Mexico City, Mexico, Sept. 20, 2017. REUTERS

A man is then seen descending into the void where other children can be heard crying.

All the people in the video appeared to be civilians, suggesting their rescue efforts came soon after the quake, before first responders could reach the school.

The overall death toll attributed to the quake stood at 217 early on Wednesday morning, but hundreds of people were still trapped in Mexico City, and surrounding areas and rescue efforts were ongoing.