The detention of undocumented immigrants has "exploded" since President Donald Trump took office and 40 new holding facilities have opened since 2017, according to a report published on Thursday.
Most of the newly-opened detention centers are run by private companies, according to the report by the American Civil Liberties Union, Human Rights Watch, and the National Immigrant Justice Center.
"The detention machine has exploded, resulting in billions of dollars in revenue for private operators," they said.
The report found that on average, Immigration and Customs Enforcement (ICE) was detaining more than 50,000 people each day in fiscal year 2019.
At times during the year, the report said, the detained population per day exceeded 56,000 people -- about 50 percent more than the previous highs during the Barack Obama administration.
It said the Trump administration has requested $4.1 billion for ICE in fiscal 2021 with the aim of expanding the agency's daily detention capacity to 60,000 people.
The report said that when Customs and Border Protection (CBP) facilities are included, the government detained some 80,000 people at a time — "far higher than the number detained in previous administrations."
Trump made cracking down on illegal immigration one of the main planks of his 2016 election campaign, including a pledge to build a wall along the US-Mexico border.
The report said there were currently 220 detention facilities in the United States and as of January 2020, 81 percent of detained people are held in facilities owned or operated by private companies.
"Immigrants in detention centers opened under the Trump administration are extremely isolated from access to counsel," said the authors of the report, who visited five detention centers and interviewed more than 150 detainees.
They said many of the facilities provided "inadequate medical care" -- even before the outbreak of coronavirus.
"People detained at all detention centers raised serious concerns about sanitation in detention and their ability to maintain personal hygiene," the report said.
According to ICE figures, 449 detainees and 36 guards have contracted COVID-19.