A fight broke out at San Quentin State Prison Thursday in what was described as a large scale incident involving between 100 and 150 inmates.
Prison staff responded in force to the melee around 11:30 a.m., according to Sgt. Gabe Walters. The fight reportedly happened in an exercise yard in the prison's reception center.
By 1 p.m., the prison was determined to be under control, according to officials.
Several inmates were slashed and or stabbed multiple times and the conditions of the four inmates still being treated for non-life-threatening injuries is unknown, Walters said late Thursday.
None of the prison staff suffered any injuries.
No shots were fired. Instead prison staff used chemical agents, non-lethal and lethal force to quell the incident, Walters said.
Officials said the prison was not technically under a lock down, but rather on a modified program in which inmates have been sent back to their cells.
The prison currently houses 4,113 inmates, including those on Death Row. It employs nearly 1,700 people.