Department of Homeland Security plans to purchase and operate mega warehouses to use as immigration detention centers are raising concerns among lawmakers, local residents and government contractors.

The proposed centers are so large that some could house as many as 8,000 detainees at once, according to a DHS spreadsheet of more than 20 potential locations that was verified by NBC News. The largest federal prison in the U.S., for example, has roughly 4,000 inmates.

At least two facilities have already been secured.

One is outside Phoenix, where Immigration and Customs Enforcement paid $70 million for a building the size of seven football fields, according to NBC affiliate KPNX of Phoenix. ICE purchased the 418,000-square-foot warehouse in an industrial park in Surprise.

Surprise city officials said in a statement that they were not aware of the purchase, that they had not been notified of it and that they had not been contacted by DHS or any other federal agency.

The other is outside Philadelphia, where ICE bought a warehouse for $87.4 million last month for possible conversion into an immigration detention center, according to NBC Philadelphia.

President Donald Trump said in an interview with NBC News on Wednesday that his administration could use a “softer touch” on immigration enforcement after federal agents shot and killed two U.S. citizens last month in Minneapolis. But Trump also said he hopes to push his immigration crackdown into five more cities.

And as the administration’s expanding plans for mass immigrant detention, which NBC News first reported in November, are coming into sharper focus, concerns are only growing.

Pro-immigrant community groups in Colorado, Mississippi and Arizona have already voiced opposition, and Arizona lawmakers said they worry the purchase of the massive building would mean aggressive immigration enforcement was coming to their area, KPNX reported.

In Hutchins, Texas, on Wednesday night, the League of United Latin American Citizens and state officials demonstrated against a proposed ICE facility.

Sen. Roger Wicker, R-Miss., said in a statement Wednesday that he strongly opposed the possibility of a detention center near Byhalia, Mississippi.

“I am all for immigration enforcement, but this site was meant for economic development and job creation,” he posted on X, along with a letter to Homeland Security Secretary Kristi Noem. “We cannot suddenly flood Byhalia with an influx of up to 10,000 detainees.”

Democratic lawmakers have criticized a proposed facility in Roxbury, New Jersey. And immigrant advocates say a possible detention center in Hudson, Colorado, a rural area more than 30 miles from Denver, would mean lawyers and family members would have difficulty visiting, in part because there is no good public transportation that far away from the city, according to NBC affiliate KUSA of Denver.

To win an ICE warehouse contract, a company must already be doing business with the U.S. Navy or partner with companies that do business with the Navy, according to an executive at a company that houses detainees and is under consideration to run one of the new ICE warehouses. The process was similar when the Trump administration built its largest detention center to date — a sprawling tent facility in Texas.

Two government contractors told NBC News they were worried that new warehouses — and the large numbers of immigrants who would be housed in them — would present safety problems.

Hiring staff members for more than 2,500 people, especially in more rural areas, would be very challenging, an executive said.