Two inmates at the Atlantic Institution in Renous have been injured following a fight at the federal prison on Wednesday.
Correctional Service Canada says both inmates were evaluated by staff and one was transported to hospital for treatment.
Prison officials say the inmates involved have been identified and appropriate actions have been taken.
The warden has ordered a lockdown and a search is underway in part of the prison.
Normal operations will resume when it is considered safe to do so.
RCMP are also involved in the investigation.