At least 20 inmates have been killed by fellow prisoners in South Carolina prisons since the start of 2017.

Seven inmates have been killed and 17 more injured at a maximum security prison in the US state of South Carolina after infighting broke out on Sunday evening.

The fighting went on for eight hours before the authorities quelled the riots.

Lee County Coroner Larry Logan told the Associated Press news agency that he arrived to a chaotic scene of fights at Lee Correctional Institution in Bishopville, which houses about 1,500 inmates – some of South Carolina’s most violent and longest-serving prisoners.

Logan said some of the seven killed died of slashing or stab wounds made from homemade knives while others were likely beaten to death.

An inmate who spoke to AP on condition of anonymity, said that bodies were “literally stacked on top of each other”.

{articleGUID}

He explained that many cell door locks were already broken before the riot and that prisoners roamed around freely.

Hours after violence broke out, no correctional officers or medical personnel attended to the dead or dying.

“It’s been over two hours, but no COs (corrections officers) have responded to this unit, and no medical personnel have attempted to render any kind of aid,” the inmate wrote to AP.

“The COs never even attempted to render aid, nor quell the disturbance. They just sat in the control bubble, called the issue in, then sat on their collective a**es.”

Following the riot, South Carolina Governor Henry McMaster’s spokesperson Brian Symmes told AP that the governor has “complete confidence” in Bryan Stirling, who has served as the head of the state’s prison system since 2013.

State officials have promised to make the prison safer after deadly fights broke out in the past few years, but have failed to do so.

Last month, several inmates took an officer hostage and took control of a dormitory for more than an hour.

In July, an inmate was killed during a fight, another was stabbed to death in November and last February, a third prisoner was killed.

In 2015 two officers were stabbed in a fight.

The year 2017 may have been the deadliest year in the history of South Carolina’s prison system, according to journalist Steve Bailey.

In the last two years, there has been a surge in inmate-on-inmate assaults.

“Put simply, anyone who can has a knife. There were 250 assaults that required taking inmates to outside hospitals in 2016 and 2017. That was more than double the previous two years,” Bailey wrote in an article for South Carolina’s Post and Courier daily newspaper.

Last year 18 people died in state prisons – 12 of them murdered by their fellow inmates, six others by suicide, according to a Freedom of Information Act request retrieved by Bailey.

The body count has risen four years in a row, Bailey noted. The record in 2017 surpassed 2016’s when five inmates were murdered and six committed suicide.

In 2009 there were two deaths in total.

“Keep in mind the prison population has fallen every year since 2010 as the state has diverted low-level offenders from the system, a good thing,” Bailey wrote.

This year so far has been even worse, with a jump in suicides.

@BryanStirling if you can’t properly handle the job that Nikki gave you, then let’s get someone in who can. These inmates still have rights and shouldn’t be dying regularly under your supervision. — Just Devin (@Devin_gain) April 16, 2018

According to Andrew Cohen, senior editor at the Marshall Project, a nonprofit news organisation covering the US criminal justice system, there are numerous factors that add to the anger and frustration boiling over in prisons – the overcrowding of inmates in deplorable conditions, understaffing of guards and poor or non-existent medical and mental healthcare.

{articleGUID}

“South Carolina officials have been aware that serious problems exist here,” Cohen said.

“They’ve seen other spasms of violence in the past few years and they’ve read the court rulings calling out the abuse and neglect and lawlessness in the prisons and they know from experts what it would take to begin to fix it, but legislators have not been willing to spend the money it would take to do the job.

“This is true even where the corrections union is pressing for more money for more and better-trained guards and staff.

“One question now is why it took prison officials so long to quell this fight and whether guards in some way just let the inmates go after one another instead of interceding. … It’s odd, I think, that so many inmates would be dead and injured and not a single guard would be injured.”

Cohen said he hopes to see a legitimate and independent inquiry take place.

After an 11-year class-action lawsuit, a 2016 ruling demanded the state to upgrade its mental health treatment. South Carolina Judge Michael Baxley wrote that the state’s care of mentally ill inmates amounted to cruel punishment.

“Evidence, in this case, has proved that inmates have died in the SC Department of Corrections for lack of basic mental health care,” Baxley wrote in his 45-page order in 2014.

The US has the highest incarceration rate in the world, with around 2.15 million people imprisoned.