The news organisation reported on Monday that inspectors with the department's internal watchdog who visited the site on May 7 found more than half of the 756 immigrants being held at the facility were kept outside, and those inside were held in cells packed at five times their capacity.
Cells were so crowded - 155 adult males in a contained area meant to hold 35 people - that the men could not lie down and temperatures swelled to more than 80 degrees Fahrenheit (27 degrees Celsius), the Department of Homeland Security's inspector general found, according to the internal report, NBC said.
Only four showers were available for the migrants at the facility, which was not named, the report said.
"With limited access to showers and clean clothing, detainees were wearing soiled clothing for days or weeks," NBC quoted the report as saying.
NBC also reported that agents working at the centre feared the conditions might lead to riots or hunger strikes.
The report was obtained by the nonprofit MuckRock through a Freedom of Information Act request.
Conditions at other facilities
Conditions at US facilities holding migrants have become a flashpoint in recent weeks after lawyers last month raised the alarm over squalid conditions facing children at another facility near El Paso. Children at that centre in Clint, Texas, told lawyers they were not given adequate food and water and often went long periods of time without a shower. US officials later relocated nearly 250 migrant youths.
At a news conference on Friday, acting Homeland Security Secretary Kevin McAleenan denied the lawyers' allegations and defended operations at the Clint facility. McAleenan said that the reports regarding the Clint centre were "unsubstantiated".
The US Congress last week passed a $4.6bn aid package to address a migrant surge at the US-Mexico border as a wave of Central Americans seek to reach the US.
Some Democrats in the US House of Representatives had pushed for the legislation to include additional protections for migrant children, but the bill ultimately passed without them.
President Donald Trump has made cracking down on immigration a cornerstone of his administration.
Representatives for the DHS could not be immediately reached for comment. The department did not respond to NBC's request for comment, according to the news outlet's report.