A crew from Huntingdon was called to Envar Composting, in Somersham Road, at about 6pm on December 31 and arrived to find a compost heap measuring about 20m by 10m aflame.
According to a spokesman for Cambridgeshire Fire and Rescue Service, the crew left the scene as the fire was left to burn out under the supervision of site staff.
On Wednesday (January 2) the fire developed, and the service increased its presence onsite.
The fire was affecting 4,500 square meters, involving approximately 3,000 tonnes of waste.
Residents and motorists in the immediate area were advised to keep doors and windows closed due to the smoke and odour. Road users were advised to drive carefully around the area, due to thick smoke.
Fire crews returned to the site on Thursday and Friday to monitor the blaze as it continued to burn under the supervision of staff.
The cause of the fire remains under investigation.