A guard taken hostage at a South Carolina maximum-security prison was rescued early Wednesday after a six-hour standoff in the prison’s most secure unit.

The lockdown at the Lee Correctional Institution near Bishopville ended around 3:15 a.m. when about 100 correction officers and state law enforcement agents blew open the door and regained control of the prison wing, housing mostly inmates serving life sentences, Department of Corrections spokesman Clark Newsom told the Associated Press.

The guard, who had been handcuffed and dressed in an inmate’s uniform to disguise him, appeared to have suffered a minor head injury and was taken to a hospital for evaluation. His name has not been released. No inmate injuries had been reported as of Wednesday morning. 

The incident began around 9 p.m. Tuesday, when a group of inmates in the special management unit of the jail attacked the guard while he escorted a nurse who was distributing medication.   

Medication is typically distributed to inmates through a slit in the door, Newsom said, but “for some reason, a door between the nurse and a corrections officer was opened.” An undetermined number of inmates then seized and beat the unarmed guard. The nurse escaped, prison officials said. 

Newsom said inmates with illegal cell phones called Lee County dispatchers about the capture of the guard. He did not know exactly how many inmates were involved in the attack, but the unit houses 116 inmates.

Not all of the inmates in the unit were involved; some barricaded themselves in their cells during the standoff, he said.

“There were ongoing conversations through the evening” with the inmates who had taken the guard hostage, Newsom said. He called the attack a “pretty disorganized effort.” After negotiations failed, that prompted police to force their way in. 

Devices were put on the doors of the facility to blow them off the hinges, and officers went inside the wing, CBS affiliate WLTX reported. 

Surveillance cameras in the unit are currently being reviewed, and a number of inmates will be questioned in what’s likely to be a lengthy investigation, Newsom said.

Lee, located about 50 miles from Columbia, S.C., is a high-security facility holding some of the most dangerous prisoners in the state’s prison system, Newsom said.

“You’ve got murderers, you’ve got rapists, you’ve got some of the worst here,” Newsom said. “It could have been a whole lot worse.”

 The Associated Press contributed to this report.

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