Ten crews, plus other specialist officers, were at the scene in Padgets Lane from around 5.10am this morning.
West Mercia Police and the Worcestershire County Council travel teams are also in attendance.
Hereford and Worcester Fire & Rescue Service said the large blaze covered an area of 40m by 40m, and had spread to other units. Padgets Lane is currently closed as a result of the fire.
People are being urged to avoid the area and nearby residents have been told to remain indoors and to keep all windows and door shut to avoid smoke and fumes entering their properties.
Assistant Chief Fire Officer Guy Palmer, who is at the scene, said: "We have responded with a significant number of appliances, including specialist appliances and good progress is being made in dealing with the incident."
"We would expect to be at the scene for another eight to 12 hours and there is a lot of impact on the road infrastructure around the area.
"If you are able, please avoid the area and keep your doors and windows closed if you are within the area of the smoke plume."