CRESCENT CITY, Calif. -- At least five inmates were shot during an altercation at California's Pelican Bay State prison on Wednesday, reports CBS Sacramento.

A statement from the prison says the incident started out as a fistfight between two inmates. Guards tried to intervene with batons and unspecified chemical agents, but the fight continued at the high-security prison near the Oregon border.

Groups of inmates ran toward the inmates and began attacking the guards. At that time, three guards opened fire with lethal rounds, firing nearly two-dozen rounds at the inmates using semi-automatic rifles and three hard foam rounds.

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Seven inmates were taken to the hospital with injuries, five of whom suffered gunshot wounds.

Eight staff members at the prison were also taken to the hospital with non-life-threatening injuries. Six were treated and released, while two remain hospitalized, but will be released soon.

"It's a frightening incident. It's frightening to have inmates just swarm you ... to overwhelm you and attack you," said Terry Thornton, a spokeswoman for the California Department of Corrections and Rehabilitation.

Several hundred of the prison's roughly 2,000 high-security inmates were in an exercise yard when two inmates began fighting, she said. They would not stop, and other prisoners ran toward the fight.

"They just ran toward the incident from several areas of the yard and just rushed the officers," Thornton said. "They overwhelmed them. Overwhelmed is the word I heard again and again."

Two inmate-made weapons were found. They appeared to be makeshift weapons that inmates grabbed during the fight, Thornton said, and officials did not yet know if they were used on the officers.

"One of them may have suffered a puncture wound, but we don't have confirmation on that yet," she said.

Ninety-seven inmates were isolated in a disciplinary housing unit after the assault.

"As the investigation progresses, we'll have a better idea how many inmates were actually involved. But the fact that the 97 inmates were rehoused indicates they had some level of involvement," Thornton said.

Investigators don't yet know whether it was a planned attack on correctional officers or if it was gang-related, she said.

Counselors were sent to the prison to help employees recover.

"We're encouraged that the officers weren't injured more than they were," Thornton said.