Immigration and Customs Enforcement announced on Wednesday that it would stop making arrests, except for those that are considered “mission critical,” until after the coronavirus crisis had passed.

Fear of an outbreak inside the agency’s detention centers is growing. At some facilities, detainees are being held in their cells for up to 21 hours a day, including during mealtimes — measures, according to officials, that are necessary to prevent the spread the coronavirus. But in other centers, requests for hot water or cleaning supplies are being denied because the items can be considered dangerous contraband.

No cases of the coronavirus have been reported in the detention centers and jails that house detained immigrants across the country. But 10 immigrant detainees at a contract detention center in Aurora, Colo., have been “cohorted” in an isolated dorm since Tuesday and were being closely monitored, the agency said.

The more than 37,000 people detained by the agency could be especially vulnerable if cases appear because of the tight living quarters, communal bathrooms and large, open cafeterias. And yet the measures intended to contain the virus have not only created greater discomfort in places where inmates say conditions are harsh in the best of times, but are also producing anxiety and fear.

At the Bergen County Jail in New Jersey, where ICE takes many immigrants it detains in New York City, fears of getting sick were stoked by the sight of an ill detainee who was removed by people in Hazmat suits last weekend, one inmate told his wife. The sick man was later returned to the unit without explanation. When ICE was continuing to make arrests, fears had been heightened by the arrival of newly detained men, another said on Wednesday.

Many ICE detainees say they feel like sitting ducks who will inevitably be infected. “The officials here have not said anything to us about what is happening outside, or any extra precautions that we should take,” said a 40-year-old man from the Congo who is detained in a Karnes City, Texas, facility.