Levels of violence in prisons have reached a new high with 65 assaults behind bars every day, new figures have revealed.
There were record numbers of attacks on inmates and officers in the year to June, while episodes of self-harm reached a peak.
It also emerged that assault rates in women's prisons are on the rise following several years of falls.
The revelations, which follow a slew of warnings about safety in jails in England and Wales, sparked claims of a "hidden emergency" in the prison system.
Figures released by the Ministry of Justice revealed that:
::In the year to June there were 23,775 assaults, an increase of 34% on the previous 12 months
::Assaults on staff jumped by 43% to 5,954, with 697 of these recorded as serious
::Reported self-harm incidents were up by more than a quarter to 36,440
::In the 12 months to September there were five apparent homicides - down from seven in the previous year
::In the same period there were 107 apparent self-inflicted deaths, while deaths in prison custody were up 21% overall to 324
A report from the Ministry of Justice setting out the findings said a rise in assaults in the last four years has coincided with "major changes to the regime, operating arrangement and culture in public sector prisons".
It said: "For example, restructuring of the prison estate including staff reductions, which have reduced overall running costs, and an increasing awareness of gang culture and illicit psychoactive drugs in prisons.
"As well as the dangers to both physical and mental health, trading in these illicit drugs can lead to debt, violence and intimidation."
New psychoactive substances - previously known as "legal highs" - have been cited as a major factor in the spike in violence.
The figures also revealed a rise in the rate of assaults in the female prison estate.
In the year to June there were 269 attacks on staff in female establishments, the highest number for the equivalent period in seven years.
The MoJ report said: "Although in the female estate a substantial reduction in the rate of assaults on staff had been seen from 2007 to 2009, followed by a relatively static period, since 2014 the rate of assaults on staff in the female estate has begun to show an overall trend of rising again."
Mark Day, of the Prison Reform Trust, said: "Today's figures reveal a hidden emergency unfolding in our prison system.
"This cannot be allowed to become the new normal.
"The Government's forthcoming prison safety and reform plan must get to grips with a dangerously deteriorating situation. The lives of people who live and work in prison depend on it."
Justice Secretary Liz Truss said the statistics "demonstrate the serious violence and self-harm in our prisons".
She said: "The consequences are devastating and go far beyond the confines of the prison walls, spilling out into our streets and communities.
"Prison reform is my top priority - I am committed to making prisons places of safety and reform, where our dedicated officers are given the support they need to help offenders turn their lives around.
"That is why I have invested an initial £14 million at 10 of our most challenging prisons, and shortly I will be publishing a White Paper outlining the much-needed reform across the prison estate to 2020 and beyond."