Dramatic vision has emerged of thousands of members of a caravan of Central American migrants streaming onto a bridge connecting Guatemala to Mexico, desperate to cross into the United States to find work and a better life.

US President Donald Trump warned Mexico it will send in the military if the caravan is not stopped before it reaches the US and returned at the Mexico border.

Dozens of Mexican riot police attempted to halt the huge surge of migrants, estimated to be at least 5000, as dozens violently shook fences and jumped into the Suchiate river below to swim towards rafts while others turned back toward Guatemala.

Many migrants with children and luggage, desperately fatigued and hungry after days on the road, simply sat down on the bridge as reports emerged police had used teargas in a bid to disperse the crowd.

Vía @AFP:

VIDEO: Drone images of thousands of migrants on the border bridge between Guatemala and Mexico pic.twitter.com/cANi68rUUL

— Webcams de México (@webcamsdemexico) October 20, 2018

The 3200km US–Mexican border is one of the busiest in the world, processing thousands of commuters daily and much of the half-a-trillion dollars of annual trade between Mexico and the United States.

Jose Brian Guerrero, 24, from Honduras, told reporters he was travelling with neighbours and his extended family in the caravan to escape violent street gangs, poverty and to find work.

“There’s nothing for us in our country,” said Mr Guerrero, who used to sell beans in Honduras.

Migrants attempt to flee Mexico riot police reportedly using teargas to disperse the crowd. Photo: Getty

Speaking in Scottsdale, Arizona on Saturday (Friday local time), Mr 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.”

….In addition to stopping all payments to these countries, which seem to have almost no control over their population, I must, in the strongest of terms, ask Mexico to stop this onslaught – and if unable to do so I will call up the U.S. Military and CLOSE OUR SOUTHERN BORDER!..

— Donald J. Trump (@realDonaldTrump) October 18, 2018

Meanwhile on Saturday (Friday night local time), Honduran President Juan Orlando Hernandez said he spoke 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.

“We’ll continue this operation for as long as is necessary,” Mr Hernandez said in a post on Twitter.

Honduras, El Salvador and Guatemala are among the poorest and most violent countries in the Americas.

Their emigrants make up the bulk of people now caught trying to enter the US illegally every year.

https://twitter.com/KTHopkins/status/1053161424544034822

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 in late March, which also drew the ire of the US president.

In the caravan, Central American migrants hiked from Honduras through muddy jungle and residential streets, some toting babies along with backpacks.

Women and children fleeing violence and poverty yell out ‘we are hungry’ as they try to cross into Mexico. Photo: Getty

In Guatemala City, where migrant shelters filled with people, waves of people departed at daybreak on roads leading to Mexico.

The nearest border is about 177 km away.

“If we don’t get across, we’re going to try the same thing again,” said Gustavo Perez, a Honduran builder speaking at a shelter in Guatemala City.

“We hope that in this big caravan group, they let us in,” he added, referring to the United States.

Mexican riot police turn around hundreds of migrants, winning praise from the US president. Photo: Getty

Mr Trump, who has vowed to curtail immigration and build a border wall on the US-Mexico border, threatened earlier this week to halt aid if Central American governments did not act.

Frustrated by Congress’ failure to fully fund his proposed wall, Mr Trump in April ordered National Guard personnel to help secure the border in four southwestern US states.

In a string of tweets, Mr Trump also said the border issue was more important to him than the new trade deal with Mexico to replace the North American Free Trade Agreement.

-with agencies