There was an average of 70 assaults a day in England and Wales prisons last year.
Violence behind bars is on the rise with assaults reaching record highs.
The situation has been blamed on overcrowding as “alarming” figures show there were more than 26,000 assaults in prisons in England and Wales last year, an average of 70 per day.
Incidents of self-harm were up by almost a quarter, reaching a record of 40,161.
Assaults on jail staff rose by almost 40% on 2015, statistics released by the Ministry of Justice show. There were 6,844 attacks on staff, of which 789 were serious.
Serious assaults against staff increased by a quarter on the previous year and have trebled since 2012.
Deaths in custody rose by a fifth to 344 for the 12-month period to March this year, of which 113 were self-inflicted.
Surging levels of violence behind bars have prompted fears of a safety crisis, with a number of major disturbances in recent months.
A 12-hour riot broke out at HMP Birmingham in December, during which staff were pelted with missiles and paint.
A month earlier, around 200 inmates went on the rampage at HMP Bedford days after a national response unit had to be sent in to control prisoners after a six-hour incident at HMP Lewes in East Sussex.
Prison officers have blamed cuts to staffing levels across the country for a breakdown in the relationship between officers and inmates.
Peter Dawson, director of the Prison Reform Trust, called on the next government to reduce the number of people in jail. He said: “The message from these deeply alarming numbers could not be any clearer. An overcrowded prison system cannot cope with the number of people it is expected to hold.
“People are being maimed and dying in unprecedented numbers as a direct consequence. Two years of positive rhetoric from the Government about prison reform has done nothing to stop a relentless decline in safety. There is no end in sight, and a new government must make a reduction in imprisonment a top priority.”
There was a decrease in all types of assault for the period from October to December last year – the first such drop since the same period in 2014.
A report setting out the figures from the MoJ said the fall “should be considered with caution due to potential seasonal effects”.
Labour shadow justice secretary Richard Burgon said: “Under the Tories, prison violence, suicide and self-harm are all out of control. They have no solution to a prison crisis which is of their own making.”
A Conservative spokesman said: “We are committed to investing an extra £100 million every year in our prisons which will reduce violence, cut re-offending rates and make our communities safer. We are recruiting an extra 2,500 prison officers to make sure offenders get off drugs and get the training they need to get jobs on the outside and quit crime for good.”