Major damage has been caused to the Cambridge OPP detachment on Beaverdale Road.
Officials say a fire broke out around 2:30 p.m., and everyone managed to get out safely.
Firefighters are still on scene dealing with hot spots.
OPP say the detachment's roof has completely collapsed.
"It's a very volatile situation," says OPP Sergeant Kerry Schmidt.
Schmidt says they have contingency plans in place, and officers will work out of the OPP detachment in Milton.
The fire marshal has been called in to investigate the cause of the blaze. There's no word on damages at this time.
Beaverdale Road is expected to remain closed between Stager and the Hespeler Road roundabout until late Tuesday evening for the investigation.
with files from Erin Anderson