Transcript for Rescuers search for survivors after Mexico earthquake

We're following multiple breaking stories. The entire island of Puerto Rico in the dark after hurricane MARIA. The governor was even out doing his best to help people rescuing people. They need as much help as they can get. There is an urgent serve under way for schoolchildren who are still trapped in the rubble from that earthquake. That is a live look at it right now in Mexico City. A desperate effort to free a young girl and the classmates who may be trapped with her. Crews have been working all day through the night, 36 hours straight so far. Our senior national correspondent Matt Gutman on the scene in Mexico City. Good morning, magnitude. Reporter: Hey, good morning, George. I want to give you a sense of what's going on. This used to be the courtyard of the school. It was shaped in a "Uth and that pile the center of everybody's attention right now. Show you what's going on here, there are welders, there are carpenter, obviously professional rescuers, everybody laser focused on trying to get that little girl out of there. This morning, rescuers are tunneling ever closer to that entombed 12-year-old and at least two others. How many people do you think are inside still? We don't know yet. Probably, probably there are more people there. Reporter: Crews using infrared cameras to scan the debris and something much more basic. Their voices. Rescuers make contact with her. They talk with her. They heard her voice. Yes, yes, the rescue teams heard her voice. Reporter: Every few minutes whilss and calls for silencio, or silence. As they try to talk to her. Once in a while cheers rising in the crowd. Even teachers reportedly on hand to calm the children inside. Amid the frantic effort to rescue the children from the trapped building, what really brings everything home is where they deposited all the children's belongings here, book bag, notebooks and toys. Everyone hoping for a repeat of this rescue. Neighbors plucking kids from the debris dusty and screaming but alive. 21 other children and four teachers died here. Over 200 killed in Mexico in that 7.1 magnitude quake on Tuesday. But as the army of rescuers burrow towards those trapped overnight, a moment of panic. Something's happening here, they say. The air suddenly filling with dust. A rescuer says the back part of the building is collapsing. Experts say those trapped in the rubble can usually survive for a week, maybe more. Helping raise their chances for survival access to water, oxygen and the temperature in that space. Now, this is still a very precarious situation for all of the workers here. One of the reasons you don't see anybody on that pile right now is because just moments ago there was a warning that it subside and shifted a bit so there is a concern that either the people inside could be hurt or the rescue workers and just overnight we had seismic warnings. Everybody in this courtyard had to be cleared out. I want to give you a sense of how precarious it is. See that building. That is what's left of the school being propped up by wood and steel beams. There was concern that that might also come down. So still loots of concern here. Not only for the people inside but the workers here. George. Matt, presumably it's taking so long because that building is so fragile right now. Reporter: That's right. Basically what they've been trying to do is build it from the outside in. That's why you see so many carpenters and can see welders. Trying to prop it up so they can tunnel through and you see that building up there. That's how high it used to be. It used to be three stories so think of condensed three-story building basically pure concrete and the problem is what they want to do is try to get those children out and want to get them out alive so dug three holes in the building. Not just about getting them out but getting them out safely and without hurting them any more than they've already been injured, George. Since they've been able to dig holes are they able to pump oxygen down there, water, food, anything like that? Reporter: They've been trying to get oxygen, water. They can't get food down there. The spaces are just far too tight and still too dangerous but know for a fact that little girl is still alive and apparently told rescuers here who just told us that she's just tired right now. My. My goodness. The issue is it was cold outside and rained and so that also limits the time that officials and workers here have to rescue her so really the race is on right now to get to her but safely and efficiently, George. Obviously without hurting anybody else. Matt Gutman, thanks very much. You can see they're doing everything they can.

This transcript has been automatically generated and may not be 100% accurate.