President Donald Trump - who has long critiqued USA immigration policies and denigrated immigrants since the start of his presidential campaign - has made numerous baseless claims about the caravan in recent weeks, spreading alarm and touting it as a "Great Midterm issue for Republicans!".
His party, the Republican Party is facing elections on 6 November and, for many Americans, immigration is a really important issue.
A caravan earlier this year that brought several hundred people to the U.S. -Mexico border (out of more than 1,000 who were at one point participating) wound up near Tijuana.
Central American migrants making their way to the U.S.in a large caravan rest under a statue of Mexico's first Indian president Benito Juarez in Tapachula, Mexico, Sunday, Oct. 21, 2018. Organizers plan for them to begin moving north, reaching the northern city of Huixtla, which is about 20 miles north, and resting there.
He also again said Democrats are to blame for not working with his administration on immigration reform.
Mexican authorities had managed to block the migrants on the Mexico-Guatemala border after they burst through a series of barriers on the Guatemalan side on Friday. In 2016, which was a record year for Guatemala and Honduras, the total number for the three nations was $419,068,700.
In another tweet, he blamed Guatemala, Honduras and El Salvador for not stopping people from leaving their countries.
"IOM reports that large numbers of people are arriving in Mexico today and are likely to remain in the country for an extended period", United Nations deputy spokesman Farhan Haq said, urging that they be treated with "respect and dignity".
"We are not criminals, we are workers!"
The president of Honduras has urged his citizens not to join the caravan.
Members of the caravan, exhausted from the hours-long trek on foot from the Guatemalan border, mostly ignored police offers to board buses heading to a migrant shelter because of suspicions they might be deported instead. He also blamed Democrats for the current immigration laws, though Republicans now control both chambers of Congress and the White House. "And as far as I know there are no terrorists in these four countries, at least beyond the corrupt governments".
In southern Mexico, police in riot gear shadowed the caravan's arrival along a southern highway, but did not impede their journey.
They stretched out overnight on rain-soaked sidewalks, benches and public plazas in the city, worn down by another day's march under a blazing sun.
Keeping together for strength and safety in numbers, some migrants huddled under a metal roof in Tapachula's main plaza Sunday night.