The fire began Friday just after 4 a.m. at the facility at 23347 McKay Ave.
Flames, sparks and smoke could be seen spitting out of a conveyor belt leading to the dust collection equipment.
Maple Ridge firefighters used a ladder-mounted hose to extinguish most of the flames from above.
RCMP confirmed that nobody was at the mill when the fire started, as the facility was shut down for the night.
The operators say it will be closed for at least a day, starting Friday.