About 2,000 migrants left the southern city of Tapachula near the Guatemala border last weekend.
The caravan appeared significantly larger and its leaders estimated its size at 4,000, more than a quarter of them children.
Officials said 1,500 young people were among the migrants. More than 1,200 of them were below the age of seven.
This is the biggest group moving through southern Mexico toward the U.S. since the pandemic started early last year.
Other groups composed mostly of Haitian migrants that have walked out of Tapachula this year have numbered in the hundreds.
All were dispersed by Mexican authorities, sometimes by force.
This caravan is primarily made up of people from Central American countries.
Without any issue, the migrants passed a customs, immigration, and military checkpoint where authorities typically seize drugs and look for human smugglers.
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