Staff at the Bathurst Correctional Complex have contained an incident involving 76 inmates in the jail’s accommodation unit, NSW corrective services says.
The ABC has been told about half the prison was locked down during the 90-minute operation.
Inmates have now returned to their cells and the jail is no longer in lockdown.
The ABC understands the prison’s Immediate Action Team was called in and gas was used to try and diffuse the situation.
The union representing prison officers said at least one officer had been injured.
It is understood the incident was sparked by an argument between two inmates, and other prisoners became involved when staff tried to calm down the initial fight.
The general secretary of the Public Service Association, Stewart Little, said an incident like this was symptomatic of overcrowding.
“The inmates involved have variable classifications so you do have some maximum security inmates in there along with minimum and medium security inmates,” he said.
“But obviously the situation at the moment within all the jails is quite tense because of the overcrowding situation.
“We’ve been concerned for some time that a situation like this could arise.”