Prisoners at HMP Liverpool are "self-isolating" to stop the spread of coronavirus, the prison told family members.
The Walton prison confirmed no prisoners had tested positive for coronavirus, although there are some quarantining themselves as a precaution.
Writing to loved ones, the prison's governor, Mark Livingston, said he could not "even begin to imagine what a worrying time this must be".
Mr Livingston said from now on social visits will not be allowed at the category B/C prison.
The letter, which was posted on Twitter, said: "I cannot even begin to imagine what a worrying time this must be for those of you who have a loved one held in HMP Liverpool at the moment.
"There will be enough going on in your day-to-day life already and I really can appreciate this will be adding additional layers of stress.
"The decision to put in place a temporary restricted regime, which included stopping social visits, was not one which was taken lightly.
"The sole objective of these changes are to implement the Public Health England principles of social distancing aiming at flattening the spread of the covid-19 virus.
"This is an extraordinary measure during a period in which the nation faces an extreme public health threat."
Mr Livingston added he "knows how difficult this will be".
He also paid tribute to the staff who are "leaving their own families each day" to come and care for the men living in the prison.
He added: "I am incredibly proud of them and I can tell you that they are 100% focused on supporting the health, mental and physical well-being of those in our care."
As well as staff caring for prisoners, Mr Livington said the facility is constantly being cleaned and everyone is practising good hand-washing.
For those tho are concerned about a loved one, Mr Livingston said the prison can be contacted on 0800 528 0970.
