A lockdown and search have been underway at Dorchester Penitentiary since Monday and all visits suspended after an inmate was assaulted, Correctional Service Canada announced on Friday.
No details about the assault at the multi-level security prison or the condition of the victim have been released.
But the circumstances will be reviewed and appropriate measures taken to prevent future incidents, Émile Belliveau, the assistant warden of management services, said in a statement.
The lockdown was implemented around 1 p.m. Monday, and the search was ordered "to ensure the safety and security of the institution, its staff and inmates," the statement said.
Normal operations will resume as soon as it is considered safe to do so, said Belliveau.
People who have already planned a visit are asked to contact the institution directly.
Dorchester houses up to 699 inmates — 397 in medium security and 302 in minimum security.