They say the inferno at the Giorgi Mushroom Company in Ruscomb Manor Township was sparked by an electrical malfunction in a utility room.
The blaze broke out at around 7:00 p.m. Wednesday.
Reports said flames shot as high as 20 feet in the air and the plume of smoke could be seen several miles away in Reading, Pa.
The multi-alarm blaze closed a part of Route 73 near Hartz Road.
No one was injured.
Damage to the facility is estimated at $300,000.