The Department of Justice says a male offender was assaulted by three other offenders at the Central Nova Scotia Correctional Facility in Dartmouth.
The assault took place shortly after 5:30 p.m. on Thurs., Sept. 21.
READ: Serious concerns about solitary confinement at Burnside jail raised after Supreme Court ruling
The injured man was treated by on-site medical staff at the facility and later transported to hospital, where he remains.
Officials are not saying how the man was injured.
WATCH: Inmate who was released early from Burnside jail found
Halifax Regional Police are investigating the incident.
The justice department says an internal review by Correctional Service is also underway.
READ MORE: N.S. justice minister rejects Opposition calls for review of Dartmouth jail