After a large fight broke out Thursday, the Oregon State Penitentiary in Salem is on indefinite lockdown.

Authorities say the fights broke out shortly after noon Thursday, with at least six inmates were separated.

Then, once that altercation was averted,  at least 75 uninvolved inmates in the recreation yard began fighting.   Officials say the prison will be on lockdown til further notice, and visitation will be cancelled.

One warning shot was fired, and chemicals sprayed on the rioters to break them up.  It's the largest disturbance in many months at the state's largest prison, housing over 2,000 inmates.

Several injuries to inmates and officers were reported, but none were deemed serious.  No word yet on why it happened.