President Trump threatened on Thursday to shut down the southern...

More than 100,000 illegal immigrants are poised to cross the US border into Texas — a crisis threatening to overwhelm facilities operated by the feds as well as shelters run by cities near the border, according to shocking new reports.

That’s the biggest monthly total in more than a decade, according to USA Today.

“It’s staggering,’’ the city manager of McAllen, Texas, Roy Rodriguez, told station KETK. “Really, we’ve never seen anything like this before.’’

US Customs and Border Protection Commissioner Kevin McAleenan said the border has hit “its breaking point.’’

He added “CBP is facing an unprecedented humanitarian and border security crisis all along our southwest border, and nowhere has that crisis manifested more acutely than here in El Paso.”

The majority of illegal immigrants turn themselves in to Border Patrol agents as asylum-seekers.

On Friday, President Trump threatened to close down the entire border unless Mexico stops the massive flow of undocumented migrants, many of them from Central American countries.

More than 36,000 migrant families arrived in the El Paso region in fiscal year 2019, compared with about 2,000 at the same time last year, according to the El Paso Times.

McAleenan said many refugees are suffering from contagious diseases. He fears crowded detention centers will make matters much worse.

“We are doing everything we can to simply avoid a tragedy in a CBP facility,’’ McAleenan said, according to Fox News. “But with these numbers, with the types of illnesses we’re seeing at the border, I fear that it’s just a matter of time.”

The report added that some 750 border agents have been reassigned to the crossings nearest to El Paso, forcing other checkpoints to close down because of a lack of staffers.

Department of Homeland Security Secretary Kirstjen Nielsen said Friday the possibility of closing the border with Mexico is “on the table,’’ Fox News reported.

She spoke following Trump’s tweet warning, “If Mexico doesn’t immediately stop ALL illegal immigration coming into the United States [through] our Southern Border, I will be closing . . . the Border, or large sections of the Border, next week.’’

Nielsen, in a call to reporters, complained Thursday that unaccompanied Mexican children can be sent home — but kids from Central America are sent to facilities run by Health and Human Services, which doesn’t have enough room to care of them.