A large group of Central American migrants travelling toward the US have vowed to push on towards Mexico City as troops began erecting barbed wire fencing.
The migrants have been walking for three weeks and the most gruelling days demand treks of more than 100 miles (160km).
They reached a gymnasium in Cordoba where they held a vote to cover the 178 miles (285km) to Mexico City on Monday by walking and hitching rides.
Many of the people still with the caravan have now covered more than 800 miles (1,200km) since setting off from Honduras on 13 October.
Calls have grown in recent days for buses to transport scores of people from the caravan to the Mexican capital for medical treatment, but no buses have arrived.
Some migrants have broken away from the caravan and gone ahead but many feel their chances of getting into the US are better if they go in numbers.
Luis Euseda, a 32-year-old from Tegucigalpa, Honduras, travelling with his wife, Jessica Fugon, said he would be staying with the caravan.
He said: "We think that it is better to continue together with the caravan. We are going to stay with it and respect the organisers.
"Others went ahead, maybe they have no goal, but we do have a goal and it is to arrive."
Many migrants are fleeing gang violence and financial hardship in their home countries.
Several smaller caravans of migrants have formed in Central America in recent weeks in an attempt to boost their chances of making it to the US.
Mexico's Interior Ministry estimated over the weekend that there are more than 5,000 migrants in total currently moving through southern Mexico either with the caravans or in smaller groups.
The ministry said 2,793 migrants have applied for refugee status in Mexico in recent weeks and around 500 have asked for assistance to return to their home countries.
Donald Trump has sent more than 5,200 troops to the US-Mexico border to stop the migrants entering the US.
Soldiers have been putting up barbed wire fences near the border in Donna, Texas.
The soldiers are being deployed by the Pentagon as part of a mission dubbed Operation Faithful Patriot to "harden" the southern border, supporting the border control and about 2,000 National Guard forces who have already been sent there.
In a rally ahead of the midterm elections on Tuesday, on Sunday, Mr Trump told supporters to "look at what is marching up – that's an invasion".
He said Democrats encouraged chaos at US borders because it was good politics.
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"Democrats want to invite caravan after caravan of illegal aliens into our country," he said.
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