Transcript for Inside the caravan of migrants en route to US border

I know, ginger. Thank you. Now to the humanitarian crisis over the border. A caravan of migrants trying to make their way through Mexico to the U.S., sparking a fierce political battle here just two weeks ahead of the midterm elections. President trump saying he will deploy the U.S. Military if necessary. Our chief national correspondent Matt Gutman is with the caravan there in Mexico. Good morning, Matt. Reporter: Tensions growing as Mexican police brace for another possible clash with this endless column of Central American migrants. The migrants bursting through the gate at the border separating Mexico from Guatemala over the weekend. Riot police responding with tear gas. Some jumping over the bridge to avoid the melee. This migrant caravan, miles long. Filled with families clutching children, all of them trudging on foot deeper into Mexico. Poised to try to cut them off on Sunday, hundreds of Mexican federal police bearing shields and armor, but just as the migrants approached, the officers pull back, setting up again, three miles down the road and again, retreating for the second time. Mexican immigration officials pleading with them to register for asylum, but most kept walking. President trump vowing over the weekend to greet them at the U.S. Border not with words, but with force. You have some very tough criminal elements within the caravan, but I will seal off the border before they come into this country, and I'll bring out our military. Reporter: They started out in Honduras, a week ago, 2,500 miles separating them from the United States. Footsore and weary, migrants straggled on under a merciless sun. They are carrying babies. Some of them with backpacks and plastic bags holding the absolute essentials. Many of them say they want to keep walking all the way to the United States. On Sunday, the heat turning migrants desperate, sending them scrambling for water. Mexican motorists taking pity, allowing dozens to pile in and to hang on to pickups and even semi trailers. This woman and her family had been walking since 4:00 A.M. One of many for whom returning to their home country would be a matter of life and death. For Blanca, there is a concern the gangs who killed her husband will come back for her and the rest of them, so it's not safe in their home or their city. A truck driver offered Blanca a ride, and begged her heat-stricken daughter get in, and collapsing into my arms. It's too hot on the floor. There was no ambulance in sight, no help. Now that driver we met up with him later. He dropped that girl off at an ambulance. We are told that she is okay this morning, and robin, you mentioned that humanitarian crisis that's building. I want to show you where we are. This is the main town square in the city of tapachula about 20 miles away from the border and there are literally thousands of people everywhere you look. They are literally -- I'll show you here. They are sleeping in the bushes here and this morning, you know, families are just starting to gather. There are meager possessions. They have a long road because there are no facilities here. No bathrooms, no showers and they face a potential clash with Mexican authorities later today. Robin? Mexican authorities have also offered asylum, but the migrants are leery of that offer? Reporter: Yeah. They have rejected it so far because they are concerned that it's a trick to try to deport them back to Honduras. They have also realized that the sheer numbers have offered them strength. They have literally been walking right past Mexican immigration authorities and police for the past couple of days now. Thank you so much.

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