HM Chief Inspector of Prisons Charlie Taylor said HMP Manchester was “fundamentally not safe enough for those living and working in there”.
Staff must be supported to “manage a very challenging population of prisoners”, he added.
In an urgent notification letter to Justice Secretary Shabana Mahmood, Mr Taylor said the number of weapons and illicit items found in the prison in recent months was among the highest of all adult men’s prisons and 39% of prisoners had tested positive for drug use in the last 12 months.
Mr Taylor said: “Drugs present a critical threat to the security of our prisons and it was very disappointing to see that some key measures in the physical security of a prison like Manchester, holding many men with known links to organised crime, were inadequate.”
More than half of inmates said they had felt unsafe at some point and there had been six self-inflicted deaths and three deaths with suspected links to drug abuse since the last inspection, the letter said.
Inspectors found there was a chronic rodent infestation and pillows had also been used to push into window frames to keep warm.
Lord James said an action plan to deliver urgent improvements would be published in the coming weeks.
He added: “Every day our dedicated staff do vital work keeping the public safe.
“They deserve better than being faced with conditions such as these and the constant threat of violence.”
HMP Manchester, which houses category A and B prisoners, was the scene of the longest prison riot in British history, lasting from April 1 to April 25 1990.
