The US will deploy 5,000 troops to the southern border in response to the thousands of Central American migrants headed to America — up from the initial estimate of 800, according to reports Monday.

The troops will be sent to Texas, Arizona and California and will likely staff ports of entry, at least in the early phases of the military mission, officials told the Wall Street Journal.

The Pentagon has dubbed the mission — which comes amid the midterm elections — Operation Faithful Patriot.

The troops, mostly military police and engineers, will come from roughly 10 US Army bases, the Journal reported.

US Marines will also be deployed.

It’s expected that most will serve until mid-December, a Pentagon official said.

About 1,800 troops will be sent to Texas, 1,700 to Arizona and 1,500 to California, according to the latest plans.

The staggering new number means there will be more troops at the border than there are in Syria and Iraq, the Journal said.

A Pentagon spokesman called the new troop totals “premature.”

The migrant caravan is still some 1,000 miles from the nearest US border crossing at McAllen, Texas.

Current estimates put the total at 4,000 marchers.

At one point last week, the estimate was as high as 7,200.

Many have dropped out to seek asylum in Mexico while hundreds of others have accepted government offers to return home.

Last week, it was reported that Defense Secretary James Mattis was set to send at least 800 troops to the border to provide logistical support.

The military sent some 2,000 National Guard troops to the area earlier this year.

President Trump has vowed that the migrants won’t be allowed into the country, calling the situation a “national emergency.”

Last week, he told the group to “turnaround” and “go back to your Country” — a plea he repeated in a tweet Monday.

“Many Gang Members and some very bad people are mixed into the Caravan heading to our Southern Border,” Trump wrote. “Please go back, you will not be admitted into the United States unless you go through the legal process. This is an invasion of our Country and our Military is waiting for you!”

On Sunday, some of the caravan stopped to rest in San Pedro Tapanatepec, located in eastern Oaxaca, Mexico.

A second caravan that recently formed broke through border gates in the Guatemalan town of Tecun Uman and clashed with Mexican authorities Sunday, resulting in the death of a 26-year-old Honduran man. He was struck in the head by a rubber bullet and killed.

That same day, 300 migrants left from San Salvador to also begin the long trek north.