Prisons in England and Wales are in their worst state for 10 years, with increasing violence, the chief prison's inspector has said in an annual report.
Nick Hardwick said the use of legal highs was fuelling violence, while inmate deaths and self-harming were rising, and staff attacks were also up.
Some prisons were "places of violence, squalor and idleness", he added.
Prisons Minister Andrew Selous said he wanted to create a prison system "that effectively rehabilitates prisoners".
Since 2005, prisons have been assessed on levels of safety, respect, purposeful activity among inmates and resettlement.
The report - Mr Hardwick's last before leaving his post - gave prisons in England and Wales their lowest overall grade since those measurements started being compiled.
It suggested the "most alarming" feature was the "accelerating increase in serious assaults", with the number of prison murders also at its highest level since records began.
By Danny Shaw, BBC home affairs correspondent
Government ministers don't like prison inspectors to comment on their policies: ministers believe the watchdog should stick to monitoring prison conditions and making recommendations.
But Nick Hardwick - whose five-year term as chief inspector hasn't been renewed - can't hold back any longer.
He blames much of the deterioration in jail safety on decisions made by the government since 2010 including; scaling back the prison regime, reforming the incentives and privileges scheme, cutting staff by almost a third.
Mr Hardwick says he has met Michael Gove, the new Justice Secretary, and told him that resources simply don't match the size of the population.
The alternatives are stark. Reduce the number who are imprisoned, or increase the money available.
Given the austerity programme and the Conservatives' traditional approach to law and order, neither seems very likely.
Last year, 239 men and women died in prison - 29% higher than in 2010-11 and a 6% increase from last year - National Offenders Management Service (NOMS) data shows.
The figures suggested self-harm among male prisoners had "risen steadily over the past five years", with the 18,995 incidents recorded last year - a third higher than 2010.
Assaults on prison staff also increased to 3,637 in 2014 - an increase of 28% from 2010.
Mr Hardwick said his assessment of prison environments were "consistent" with the NOMS figures.
"More prisoners were murdered, killed themselves, self-harmed and were victims of assaults than five years ago. There were more serious assaults and the number of assaults and serious assaults against staff also rose," he said.
There were not enough resources available to cope with the size of the prison population - which had increased to 87,000 - Mr Hardwick said.
Yet between March 2010 and December 2014 the number of full-time staff in public sector jails had dropped by 29% from 45,080 to 32,100, he said.
"It can't go on like this," said Mr Hardwick. "Prisons can't be immune from the language of priorities."
A typical week in the prisons
- Four to five prisoners die
- One or two self-inflicted deaths
- 500 self-harm incidents
- More than 300 assaults
- 40 serious assaults, often using a blunt instrument or blade as a weapon
- 70 assaults on staff, including nine serious attacks.
Source: Safety in Custody Statistics from Ministry of Justice quarterly update
The inspector also criticised a lack of rehabilitation of prisoners, despite government promises of a "rehabilitation revolution".
"It is hard to imagine anything less likely to rehabilitate prisoners than days spent mostly lying on their bunks in squalid cells watching daytime TV.
"For too many prisoners, this was the reality and the 'rehabilitation revolution' had yet to start," he added.
Mr Hardwick said he had spoken to Justice Secretary Michael Gove about the problems, adding: "The ball is in the Secretary of State's court and he needs to respond to that."
Prisons minister Mr Selous said: "The safety of our staff as they deliver secure prison regimes is our priority and we are tackling dangerous new psychoactive substances to help drive down the number of assaults and violent incidents.
"Our prisons must punish those who break the law, but they should also be places where offenders can redeem themselves."
Juliet Lyon, director of the Prison Reform Trust, said it was "no mystery that violence, self-harm and suicide rise when you overcrowd prisons, reduce staff by almost one-third, cut time out of cell and purposeful activity".
The report does not include prisons in Scotland or Northern Ireland, where services are run under devolved powers.