PIJIJIAPAN, Mexico — The main plaza in Pijijiapan quickly became a makeshift triage centre as thousands of Central Americans trudged into this southern Mexico town.

A severely dehydrated woman connected to an IV line sat on a plastic chair in the gazebo. Nearby, volunteer nurses took temperatures and treated coughs, handing out donated medicine as migrants lined up.

Two weeks of walking have taken a toll on a caravan of migrants now estimated at more than 4,000 as it slowly marches through Chiapas, Mexico’s southernmost state that is far from their goal of reaching the United States.

In the first four hours Thursday, Dr. Jesus Miravete treated more than 120 people. Many had burns on their feet from walking in plastic sandals on the steaming highway.

“So many tell me: ‘I can’t rest. I have to go on,'” Miravete said. “It’s really hard. I feel overwhelmed, above all by the number of dehydrated children I have seen.”

Yet the migrants were planning what would be their most ambitious single-day trek since they crossed into Mexico, setting their sights for Friday on reaching Arriaga, about 62 miles (100 kilometres) up the coast.

Like in many places in Chiapas, residents in Pijijiapan turned out in force to aid the travellers as they streamed in on foot, offering shelter, food and medical treatment. Some people offered rides to the plaza. Others showed up with used clothes and boxes of sandwiches.

The caravan was earlier welcomed in a similar fashion into Mapastepec, a municipality of 45,000 residents 30 miles to the south where city officials put up tents around the main square offering everything from medical attention to donated clothing to baby formula. Local churches offered free showers and set up food distribution points.

“They are human beings. You have to do something to help them,” said Cesar Cabuqui, who handed out dozens of homemade bean and cheese sandwiches and bags of water.

Chiapas is home to some of Mexico’s poorest communities. Yet the towns on the migrants’ route have organized to offer them shelter, medical treatment and donations as best they can.

Grateful for the hospitality, many of the migrants have tried to be respectful visitors.

Jose Reyneri Castellanos, from El Progreso, Honduras, hung back behind the rest of the caravan with his wife and two young sons to help sweep and tidy up in Mapastepec — as they’ve done at each stop, figuring it well help ensure a continued warm reception as they head north.

“I think it is important to leave the community and the city clean,” Castellanos said.

Many of the migrants say they are dreaming of finding better lives in the United States. They say they have been driven to leave their homelands by severe poverty and rising gang violence.

Such caravans have taken place regularly, if on a smaller scale, over the years, but U.S. President Donald Trump has seized on the phenomenon this year. He has been warning about this caravan and illegal immigration, repeating hitting Democrats on the issue as the U.S. heads into the hotly contested Nov. 6 midterm elections.

Defence Secretary Jim Mattis was expected to sign an order to send 800 or more additional troops to the southern border to support the Border Patrol, according to a U.S. official, who spoke on condition of anonymity because he was not authorized to speak publicly because the details had not yet been finalized.

The caravan is still some 1,000 miles from the nearest border crossing at McAllen, Texas, but the journey could be twice that if the migrants head to the Tijuana-San Diego crossing. That was the destination of a smaller caravan earlier this year, and only about 200 in the group made it.

This group also has begun to thin. Authorities say 1,740 have applied for refuge in Mexico and hundreds more have taken up offers of bus rides back to Honduras. Sickness, exhaustion and police harassment have helped whittle down their numbers.

Immigration officials appeared to be intervening more aggressively with the migrants’ movements amid the sweltering 90-degree heat.

A taxi driver in Mapastepec said he had seen immigration agents force migrant passengers out of cabs at a checkpoint.

An official from the country’s Human Rights Commission said migrants could go through if they were in vans or trucks that offered them free rides, but if they had paid they would have to get out because of insurance regulations.

On Thursday, the long column stretched for miles along the highway. Families with young children packed sidewalks asking for donations and rides.

Candy Guillermo, 37, said she had heard from others in the caravan about Trump intending to send U.S. troops to the border. A single mother of four, she was puzzled that the leader of such a powerful country would find her and the families travelling alongside her a threat.

“It surprises me because there are children here. President Trump should be more humanitarian,” Guillermo said, wiping sweat from her brow. “We only want to give our kids a better future.”

Christopher Sherman And Julie Watson, The Associated Press