President Trump said the USA will "turn away" the thousands of Central American migrants heading to the USA border in search of asylum and blamed Democrats for being weak on immigration.
Most of the migrants on the move on Sunday - by one local government estimate more than 7,000 people - had crossed the border illegally in recent days by swimming or rafting across the Suchiate River, which separates Guatemala from Mexico.
FILE - Mexico's President-elect Andres Manuel Lopez Obrador speaks during a rally as part of a tour to thank supporters for his victory in the July 1 election, in Acapulco, Oct. 3, 2018.
It was not immediately clear where the additional travelers came from since about 2,000 had been gathered on the Mexican side Saturday night.
Ulises Garcia, a Red Cross official, said some migrants with injuries from their trek refused to be taken to clinics or hospitals because they didn't want to leave the caravan. Some carried a Honduran flag, chanting "Mexico".
As he had in prior speeches, Trump said he believed that Republicans can win in November by touting the successful confirmation of Justice Brett Kavanaugh and pushing a hard line on immigration.
Those proposals have not gotten traction among congressional Democrats, who view those changes as anti-immigrant.
After an emergency meeting in Guatemala, presidents Hernandez of Honduras and Jimmy Morales of Guatemala said an estimated 5,400 migrants had entered Guatemala since the caravan was announced a week ago, and about 2,000 Hondurans have returned voluntarily.
The Associated Press news agency says many migrants do not have passports and have been using national ID cards, which allow them to travel within Central America.
Trump added that the United States will turn migrants away if they do not apply for asylum first in Mexico.
At the Suchiate River, some 700 federal police officers from Mexico made no attempt to intervene as hundreds of young men dropped off the bridge into the water, then swam, floated or rafted to Mexico.
President Trump has threatened to call up the USA military and shut the border with Mexico to keep out the group.
But perhaps 2,000 others entered Mexico illegally and vowed to cross that country, with the USA their goal.
Olivin Castellanos, 58, a truck driver and mason from Villanueva, Honduras, said he took a raft across the river after Mexico blocked the bridge. He says it's important to help others: "Today it's for them, tomorrow for us".
"There is no work back home", he said.
Hernandez said on Twitter he had asked Guatemalan authorities "to contract land transportation for those who wish to return - and airlift in the special cases of women, children, the elderly and the sick - and we will continue with this operation as long as necessary".
"We're just making sure they pass safely and then we'll steer them" to a migrants shelter outside the city centre of Tapachula, about 32 kilometres north-west of the border, he said.
A growing crowd of Central American migrants is resuming its advance toward the USA border in southern Mexico on Sunday.
Officials said that as of late Sunday, they had received more than 1,000 asylum requests from caravan members at the border.
Francisca: I joined the caravan because I was afraid to come on my own but I want my children to have a better life than me.
Changes to detention rules saw thousands of migrant children detained and separated from their parents at the US-Mexico border earlier this year, sparking national and worldwide condemnation.
Migrants have commonly cited widespread poverty and gang violence in Honduras, one of the world's deadliest nations by homicide rate, as their reasons for joining the caravan.