About 50 firefighters are tackling a blaze at an industrial unit containing hazardous materials after explosions were heard.
The fire on Parham Airfield, near Framlingham, Suffolk, is understood to be at a vehicle components factory and broke out at about 09:45 BST.
A witness reported hearing "loud bangs and explosions", and plumes of black smoke can be seen for miles.
The fire service said no-one had been injured in the incident.
Richard Lapage, who was driving "a couple of hundred metres away", stopped his car when he heard "loud bangs and explosions".
"It's at Hatcher Components, a fibreglass place," he said.
Suffolk Fire and Rescue Service said 13 crews were tackling the "hazardous materials" fire and have urged residents and nearby businesses to keep doors and windows closed.
Suffolk Police confirmed officers were at the scene and road closures are currently in place in the area.