Northamptonshire Fire and Rescue Service (NFRS) was called to the fire shortly after 12.30pm today, Monday, May 13, and there are at ten appliances currently on the scene.
The building involved measures around 100m by 150m, and all three storeys, as well as the basement, are affected by the fire.
Residents in the local area are advised to keep their doors and windows shut, and avoid any unnecessary exposure to smoke from the fire.
No casualties have been reported as a result of the blaze, but neighbouring properties have been evacuated as a precaution.
The police, fire and ambulance services are all on scene, as well as representatives from utility services.
Northamptonshire Police has closed the following roads while the incident is dealt with:
Rockingham Road at the junction with Nelson Street
Motorists and pedestrians are advised to avoid the area while the incident remains ongoing.