
President Donald Trump renewed his claim on Monday that the sea of humanity inching its way north from Central Americato the United States is a pit of unsavory gangsters and terrorists.

Trump complained on Twitter that Mexico has been unable to stop the thousands of Hondurans and Guatemalans who have captured humanitarian interest while they've piqued his outrage.

'Sadly, it looks like Mexico’s Police and Military are unable to stop the Caravan heading to the Southern Border of the United States. Criminals and unknown Middle Easterners are mixed in. I have alerted Border Patrol and Military that this is a National Emerg[enc]y. Must change laws!' he tweeted.

The president also returned to his political messaging just 15 days before the midterm congressional election, saying voters who fear the impact of a mass influx of illegal immigrants should elect more Republicans.

'Every time you see a Caravan, or people illegally coming, or attempting to come, into our Country illegally, think of and blame the Democrats for not giving us the votes to change our pathetic Immigration Laws! Remember the Midterms! So unfair to those who come in legally,' he said.

Trump reiterated, too, his threat to pull foreign aid from Guatemala, Honduras and El Salvador, an unprecedented consequence for the developing nations whose migrant exodus has largely been controlled by drug cartels and human traffickers, not government agencies.

The Department of Homeland Security is warning that Mexico's cartels will try to 'prey on the vulnerabilities' of migrants in the caravan, now 7,000 strong.

Caravan: As many as 7,000 people are now traveling in the caravan which was seen from the air in Tapachula, in southern Mexico - still 1,600 miles from the U.S. border

On the road: The migrant caravan was in Metapa, in the southern Mexican state of Chiapas, Monday, at the same time as Trump was tweeting that it was a 'national emergency' in the U.S.

On the move: Honduran migrants used a truck to get further into Mexico in Tapachula on Monday

On their way: Members of the caravan get on the back of truck as they try to make their way north from Tapachula

Assistance: These members of the caravan had crowded into the back of a truck to get to the city of Tapachula, after crossing the border from Guatemala into Mexico

The president said Monday that he has alerted the U.S. military about a national emergency

He reminded the governments of Honduras, Guatemala and El Salvador on Monday that the aid money they get from Washington could dry up

Cool down: Central American migrants use a fire hydrant in the main plaza of Tapachala, the city just across the Mexican border where as many as 7,000 are now gathered

Crossing to Mexico: Migrants are using rafts to cross the Suchiate River, the barrier between Mexico and Guatemala, to avoid military and borer patrols

Pressure: The city of Tapachula has seen Miguel Hidalgo Park become ground zero for members of the migrant caravan sleeping rough

Impact: In Tapachula public authorities are facing huge numbers of people sleeping outside, especially in Miguel Hidalgo Park

Emergency measure: Red Cross tents have been put in place in the arena used for the annual International Mesoamerican Fair in Tapachula

Sleeping rough: One of the Honduran migrants who has made it to the border at Tecan Uman, Guatemala, sleeps as he waits for his claim to be processed

On the road: Local trucks have been moving people who started in Honduras and are now in Mexico on their way to Tapachula

Ready for arrivals: These tents have been erected at the International Mesoamerican Fair's former venue in Tapachula in anticipation of even more people crossing the border

The caravan began its march in Honduras before crossing Guatemala and into Mexico at Ciudad Hidalgo. The migrants, who are said to number up to 7,000, rested in a town called Tapachula - around 20 miles from Hidalgo - on Sunday night, and are now continuing north towards the US

The Department of Homeland Security has vowed to crack down on Mexican cartels trying to help a caravan of thousands of desperate migrants cross from Mexico into the US (pictured, part of the caravan in Mexico)

Around 3,000 people have crossed from Guatemala into Mexico since arriving on Friday, down from around 5,000 after many gave up and returned home (pictured, migrants in Mexico)

Despite being stopped by Mexican border guards, many Hondurans either swam across a river or were helped across the border by Mexicans using pickups and trucks (pictured, migrants in Mexico having crossed the border)

The caravan continued to march across Mexico on Monday despite threats from President Trump to stop anyone who had not applied for legal asylum at the US border

Dozens of migrants rest in the main square in Tapachula, Mexico, on Sunday having walked from Ciudad Hidalgo, around 20 miles away on the border with Guatemala

Migrants wave a Honduran flag having crossed the border between Guatemala and Mexico, where they have vowed to continue on to the United States

A young Honduran girl eats in the main square in Tapachula, Mexico, after successfully crossing the border from Guatemala

DHS Secretary Kirstjen Nielsen warned that criminals and people smugglers will be hunted down and 'prosecuted to the fullest extent of the law.'

Nielsen spoke as thousands marched on through Mexico toward the U.S. on Sunday after evading fences and guards along the border with Guatemala.

Up to 7,000 people are now traveling in the caravan, according to the Los Angeles Times; the Associated Press reported 5,000 and AFP counted as few as 3,000.

Several thousand are thought to have returned home, some on buses provided by the Guatemalan government, after being blocked at the Mexican border.

But a new group of 1,000 Hondurans have begun the journey, vowing to following in the footsteps of the first.

Mexican officials say 640 people stopped at their border before applying for legal refuge, including 164 women, more than 104 children and teenagers, and many older and disabled people.

Of those who managed to cross the border most ended up in a town called Tapachula, around 20 miles from the border at Ciudad Hidalgo, where they rested on Sunday night before continuing their march.

President Trump has taken an unusually hard line against Central American countries ina bid to force them to retrieve their own people instead of allowing them to march north through Mexico

They now face a daunting slog of 1,600 miles across Mexico before reaching the U.S. border, where President Trump has vowed to turn them away.

Hefired off a tweet on Sunday afternoon, saying: 'Full efforts are being made to stop the onslaught of illegal aliens from crossing our Southern Border.

'People have to apply for asylum in Mexico first, and if they fail to do that, the U.S. will turn them away. The courts are asking the U.S. to do things that are not doable!'

Mexican border guards initially drew praise from Trump for their hard line approach after stopping thousands of people from crossing into the country using riot shields and tear gas.

But many later crossed the river on makeshift rafts, or were helped across by sympathetic Mexicans who loaded them into pickups, vans and cargo trucks before driving across.

Speaking on Sunday about the group who had crossed into Mexico, Nielsen said: 'While we closely monitor the caravan crisis, we must remain mindful of the transnational criminal organizations and other criminals that prey on the vulnerabilities of those undertaking the irregular migration journey.

A pickup truck owned by a Mexican driver helps migrants to cross the border from Guatemala, followed closely by another driver doing the same thing (left)

Having already walked to Mexico from Honduras, almost 350 miles away, the migrants now face a trek of 1,600 miles across Mexico in order to reach the U.S. border

Paramedics check the blood pressure of a migrant in Tapachula, after he made his way across the border

Mexican medics treat a Honduran child in Tapachula after their family made the crossing from Guatemala at the weekend

Migrants on the Guatemalan side of the border wait to cross into Mexico after being stopped by guards

Guatemalan officials fumigate the main bridge between their country and Mexico which has been crowded by thousands of migrants in recent days

'We shall work with our partners in the region to investigate and prosecute to the fullest extent of the law all who seek to encourage and profit from irregular migration.

'We fully support the efforts of Guatemala, Honduras and Mexico, as they seek to address this critical situation and ensure a safer and more secure region.'

Aaron Juarez, 21, a migrant walking through Mexico with his wife and baby while limping from an injury, vowed that 'no one is going to stop us' from getting into the U.S. '[Not] after all we've gone through.'

Honduran farmer Edwin Geovanni Enamorado said he was forced to leave his country because of intimidation by racketeering gangs. 'We are tired, but very happy, we are united and strong,' he said.

Britany Hernandez added: 'We have sunburn. We have blisters. But we got here. Our strength is greater than Trump's threats.'

Mexico's President-elect Andres Manuel Lopez Obrador called for fair treatment of the migrants.

'We don't want them to face what (Mexicans) face when they need to look for work in the United States,' he said on Twitter.

Mexican officials question a migrant waiting to cross the border from Guatemala. Mexico says around 640 people have applied for legal asylum in their country

Central American migrants, part of a caravan trying to reach the U.S, line up as they wait for the gate to open on the bridge that connects Mexico and Guatemala

The caravan left San Pedro Sula in northern Honduras more than a week ago, following a call on social networks relayed by a former Honduran deputy.

The politician, Bartolo Fuentes - a member of leftist former president Manuel Zelaya's Freedom and Refoundation Party - told AFP he only reproduced a poster on his Facebook page.

The poster invited people on a 'Migrant march' with a slogan: 'We're not leaving because we want to, but because we are being expelled by violence and poverty.'

Morales and his Honduran counterpart Juan Orlando Hernandez said after meeting that the march was 'violating the borders and the good faith of the states.'

The Honduran president acknowledged that social problems were a contributory factor.

'Without a doubt, we have a lot to do so that our people can have opportunities in their communities,' he said.

Migrants denied their motives were political.

'We decided to join those who were going,' said Edgar Aguilar. This is not political. This comes from hunger, from the drought, it's for prosperity, for a better life. This is not political!'

The migrants are generally fleeing poverty and insecurity in Honduras, where powerful street gangs rule their turf with brutal violence.

With a homicide rate of 43 per 100,000 citizens, Honduras is one of the most violent countries in the world, according to a Honduran university study.