VANCOUVER -- Officials have placed a federal prison in B.C.'s Fraser Valley on partial lockdown as they battle a rapidly growing outbreak of COVID-19 among the inmate population.

The number of infections at Mission Institution has grown from two to 11 since the weekend, and officials confirmed Wednesday that the facility's medium-security unit has been locked down as a precaution.

"We are closely and carefully following direction from public health officials, while following strict protocols to avoid further spread in the institution," Correctional Service Canada said in a news release.

Those protocols include enhanced cleaning measures and twice-daily checks of inmates suffering from flu-like symptoms. Inmates who are asymptomatic are also being checked by nursing staff once per day, and being delivered meals in their cells.

The union representing prison guards, which has expressed concerns about staff safety at the prison, indicated there was already a lockdown at the facility as of Saturday.

The Union of Canadian Correctional Officers said guards are now being given non-surgical masks to wear in any area "that does not allow for safe social distancing," but that there is only enough supply for staff to use one for two shifts.

There are currently no masks available for prisoners, though the union said it has been told more personal protective equipment is being procured.

"We recognize that this is not an ideal situation, but one which is needed to ensure this public health advice is implemented immediately," the union said on its website Wednesday.

Across Canada, there have been COVID-19 outbreaks at four different federal prisons, including two in Quebec and one women's prison in Ontario. A total of 35 inmates have tested positive for the virus.

With files from The Canadian Press