Advocates raised alarms Friday about the health of medically vulnerable people in jails and prisons as coronavirus continues to spread in the United States.

In New York, several advocacy groups sent a letter Friday to Gov. Andrew Cuomo asking for immediate clemency for elderly state prisoners and those who are pregnant or already ill. Advocates have made similar calls for clemency for vulnerable or low-risk people nationwide.

"Elderly people and people who are medically compromised need to be released now, before it's too late," said David Patton, executive director and attorney-in-chief of New York's Federal Defenders. "We know that this poses a real threat, and if those folks contract the virus, especially if they contract it in a jail setting, their lives are at risk."

Patton said jails and prisons should be assuming that they, like any other employer in the country, will have staffing shortages as more people get sick. Reducing the number of inmates will also reduce the workload on a smaller staff and open up space to handle medical issues, he said.

Asked about the New York letter, an adviser to Cuomo noted that the state's Department of Corrections and Community Supervision released its coronavirus plan last week. The plan said visits to state correctional facilities will continue but visitors will be screened for coronavirus symptoms or exposure.

The federal Bureau of Prisons announced a 30-day suspension of visits Friday; the ban includes attorneys, but prison officials said some case-by-case exceptions for legal counsel will be considered.

Josie Duffy Rice, a lawyer and president of the criminal justice-focused publication The Appeal, said suspending visits is a flawed plan, because prison employees will still be moving in and out each day and interacting with their own families.

"This idea that just putting people on lockdown will protect them, or protect the rest of us, is wrong," she said.

Homer Venters, a doctor and former chief medical officer for New York City's Correctional Health Services, said coronavirus is likely to spread rapidly in jails and prisons.

Health care is inadequate already in jails and prisons, Venters said, to the point where even basic prevention measures are a challenge.

"We hear a lot about hand-washing as our most important tool," he said. "Most of the jails and prisons I've been to around the country don't really have enough sinks and certainly if there's a sink that works, there's often not paper towels, there's not soap."

Separating inmates who are showing symptoms of COVID-19 will be key, Venters said, but he's concerned that crowded jails and prisons won't have enough space to set people apart.

Jose Saldaña, director of the Release Aging People in Prison Campaign, which signed the letter to Cuomo, served 38 years in New York state prison and was released just over two years ago. He echoed Venters' concern about the possibility of quarantines within prisons.

"If everybody in there gets quarantined, if you don't have it, [then] you will have it," he said.

Saldaña, who is in his 60s, said he's worried about the survival of the people he spent decades with in prison, who are still there and suffering from health issues already.

"I know that their health has been compromised," he said. "They're having problems getting treatment for their conditions. You compound that with the coronavirus, that's just certain death to some of them."