Arsonists set fire to a petrol station shop in Spaldwick in the early hours of Saturday.
Firefighters from Kimbolton, Huntingdon, Sawtry and St Neots were called to a fire at a petrol station in High Street, Spaldwick, shortly before 4am.
A spokesman for Cambridgeshire Fire and Rescue said: “The main building was well alight and heavy smoke was issuing. The forecourt was not affected and fuel pumps were isolated.
“Twelve firefighters wearing breathing apparatus used hose reels and jets to extinguish the fire and positive pressure ventilation fans to clear smoke.”
The fire was extinguished by 7.25am.
An investigation revealed that the cause of the fire was deliberate.
Anyone with information should contact the police on 101 or the independent charity Crimestoppers anonymously on 0800 555111.