In tweets on Friday morning, President Donald Trump warned of a new migrant caravan forming in Honduras and vowed to close the US-Mexico border and withhold aid to Central American governments.

But the new caravan isn't heading to the US, according to immigration advocates and news reports.

The caravan is estimated to have roughly 15,000 members, most of whom are traveling to Mexico's southern states to find work.

Mexico's president has promised to grant work visas to Central American migrants.

President Donald Trump on Friday threatened to close the US-Mexico border and cut off aid to Central American countries, citing a new caravan forming in Honduras — which reportedly isn't even heading to the US.

"Either we build (finish) the Wall or we close the Border," Trump tweeted. "Honduras, Guatemala and El Salvador are doing nothing for the United States but taking our money. Word is that a new Caravan is forming in Honduras and they are doing nothing about it."

He continued: "We will be cutting off all aid to these 3 countries - taking advantage of U.S. for years!"

Trump was most likely referring to reports of a caravan of roughly 15,000 migrants set to travel north from Honduras in mid-January, according to The San Diego Union-Tribune.

Read more: As the government shutdown over Trump's border wall rages, a journey along the entire 1,933-mile US-Mexico border shows the monumental task of securing it

A caravan of nearly 7,000 migrants from Central America walk through Mexico in October. Reuters/Adrees Latif

But organizers and Spanish-language news outlets have said the caravan is planning to stay in southern Mexico, in the states of Chiapas and Oaxaca.

"We assume that this caravan ... will pick up more people in El Salvador and Guatemala," Irma Garrido, a representative for the immigration advocacy group Reactiva Tijuana Foundation, told Mexico News Daily this week. "But their aim is to arrive in Chiapas and request work there."

The new Mexican president, Andres Manuel López Obrador, has promised to grant work visas to Central American migrants fleeing Honduras, Guatemala, and El Salvador — known as the Northern Triangle — because of poverty and violence.

The previous caravans are still stuck south of the US border

A migrant girl, part of a caravan of thousands from Central America trying to reach the US, rests in a temporary shelter in Tijuana, Mexico, on November 28. REUTERS/Hannah McKay

The reports of a new caravan come as thousands of migrants from caravans that reached the US-Mexico border in the fall remain in Tijuana, Mexico.

The Trump administration has adopted a practice at the nearby ports of entry called "metering," permitting only small numbers of migrants to enter at a time to request asylum — and leaving a massive backlog of migrants waiting on the southern side of the border.

Facing monthslong delays and an overwhelmed shelter network in Tijuana, some of the migrants have crossed the border into the US illegally, opted to remain in Mexico and work, or even returned home.

Read more: The migrant mom pictured fleeing with her kids from tear gas at the US border has finally set foot on American soil

Honduran migrants climb a fence between San Diego and Tijuana on Tuesday. Associated Press/Daniel Ochoa de Olza

Garrido told Mexico News Daily that members of the new caravan in Honduras had heard rumors of "strong xenophobia" near Tijuana due to the previous caravans, suggesting it influenced their decision to remain in southern Mexico.

But Garrido added that some members could continue north to the US regardless.

Already, conservative media has begun to seize on news of the new caravan to drum up support for Trump's immigration agenda.

"Report today that another, far larger, caravan assembling in Honduras of as many as 15,000 people," the Fox News host Laura Ingraham tweeted. "About 1,000 illegals released every week. Will Pelosi & Schumer do nothing? McConnell? Hello?"

The US government entered a partial shutdown last week after Trump demanded that Congress pass a spending bill that includes billions of dollars to fund a wall along the border.