Mexican police dressed in riot gear have stopped a caravan of Honduran migrants at its border with Guatemala.
Hundreds of people in a caravan of migrants that crossed from Honduras into Guatemala have staged a dramatic bid to breach the Mexican border, as local governments began preparing to disperse the convoy under pressure from Washington.
Migrants poured through Guatemalan border posts in the town of Tecun Uman and onto a bridge leading to Mexico, only to be halted by dozens of Mexican police in riot gear.
US President Donald Trump warned the Central American caravan must be stopped before it reaches the United States, and Honduras and Guatemala said on Friday they were mobilising to assist the return of Honduran migrants to their homeland.
Some migrants violently shook fences at the border and police said a few officers were injured in clashes. A handful of migrants jumped into the Suchiate River below to swim for rafts. Others turned back toward Guatemala.
Carrying backpacks and small children, many bedraggled migrants simply sat down on the bridge. Some said that they had been teargassed. As the afternoon drew on, a tropical storm, Vicente, formed nearby off the Pacific coast.
On Friday, Honduran President Juan Orlando Hernandez said he had spoken to his Guatemalan counterpart Jimmy Morales for clearance to send civil protection personnel to help the Hondurans and to find transport for those wanting to return.
Mexican President Enrique Pena Nieto called the mass rush to penetrate the border "unprecedented", accusing some migrants of attacking police.
"Mexico does not and will not allow (people) to enter its territory illegally, let alone violently," he said.
Speaking in Scottsdale, Arizona on Friday, Trump said he "appreciated very much" Mexico's efforts to stop the caravan.
"If that doesn't work out, we're calling up the military - not the (National) Guard - we're calling up the military," he told reporters.
"They're not coming into this country."
Trump has also threatened to cut off aid to Honduras, Guatemala and El Salvador - some of the poorest and most violent countries in the Americas - if they fail to prevent undocumented immigrants from heading to the United States.
Their emigrants make up the bulk of people now caught trying to enter the US illegally every year.
Several migrants at the Guatemala-Mexico border spoke of entire neighbourhoods leaving their homes to join the trek after news circulated on social media of a call for a new "caravan" to Mexico six months after the previous one.
Hundreds of Mexican police were sent to guard the border between the Guatemalan town of Tecun Uman and Ciudad Hidalgo in Mexico to prepare for the migrant caravan's arrival.