Matsqui Institution in Abbotsford was placed on lockdown on Tuesday morning following the assault of an inmate.
Assistant warden Gordon Mattson said the lockdown was required to facilitate a search of the living units and common areas.
"The search is being conducted to ensure the ongoing safety and security of the institution, its staff and the inmates. The institution will return to normal routine when it id determined safe to do so," he said.
Mattson said regularly scheduled visits to the prison will be affected. Those who have previously scheduled visits are asked to contact Matsqui Institution.
No further details were available.