Police and justice officials are investing another assault at Her Majesty's Penitentiary in St. John's, but so far are releasing few details.
The Royal Newfoundland Constabulary confirmed there was an incident on Sunday afternoon, but is not commenting on details.
An official said more information will be made available later Monday.
A series of violent events has put security at the penitentiary under the spotlight.
Just last Tuesday, an incident saw one inmate assault another at the prison.
Two weeks ago, parts of the penitentiary were damaged after some inmates refused to return to their cells.
In February, an attack was staged at the prison chapel targeting Kenny Green, who was subsequently convicted of manslaughter in the beating death of Joey Whalen at a drug house in downtown St. John's.
Last August, a riot broke out that saw inmates threaten to kill hostages and prison guards. There was extensive damage to the prison.