Bishopville – Seven South Carolina prison inmates were stabbed to death and 17 others injured in an eight-hour-long riot that stands as the deadliest in the United States since 1993, according to state officials and a prison safety expert.

The Lee Correctional Institution in Bishopville, South Carolina, about 64 km northeast of the state capital of Columbia, was secured at 06:55 a.m. GMT, the state Corrections Department said on Twitter. The violence began around 23:15 p.m. GMT on Sunday night, spilling out over three housing units.

It was the deadliest U.S. prison riot since 1993, when nine inmates and one corrections officer died at the Southern Ohio Correctional Facility in Lucasville, said Steve Martin, a longtime prisons expert and now the federal monitor for the consent decree involving New York City’s Rikers Island jail complex.

All seven deaths were the result of stabbing injuries, said Lee County Coroner Larry Logan.

"In prison, it’s not like you have guns, or people are going to get run over,” Logan said in a phone interview.

The prison has 1,583 inmates, according to its website.

All prison staff and law enforcement officers were safe and accounted for, officials said on Twitter. They provided no other details ahead of a scheduled 17:30 p.m. GMT planned briefing with Governor Henry McMaster.

The prison population in South Carolina fell about 15 percent from 2010 to mid-2017, to 20,105, with beds being underutilised across the state, the department’s fiscal 2017 Accountability Report said.

The state has about 5,000 prison employees in 22 institutions, but "security staff numbers continue to lag behind the authorized strength,” it said, without giving numbers.

Martin said staff shortages could have been a contributing factor in the riot.

"When high-security inmates start engaging each other and there aren’t enough staff, it’s hard to stop it,” Martin said in a phone interview.

State data show there were 37 serious inmate assaults on prison employees last year, up from 21 in 2015.

State officials identified the slain inmates as Raymond Scott, 28, who was serving a 20-year sentence for crimes including assault and battery; Michael Milledge, 44, serving 25 years for drug trafficking; Damonte Rivera, 24, serving life for murder; Eddie Gaskins, 32, serving 10 years for domestic violence; Joshua Jenkins, 33, serving 15 years for manslaughter; Corey Scott, 38, serving 22 years for kidnapping; and Cornelius McClary, 33, serving 25 years for burglary.

Agencies