A spokesman said the blaze involved wooden pallets and cars, and was started at about 12.48pm.
A large plume of smoke can be seen across the city from the flames.
Six fire crews are on the scene, with firefighters from Dogsthorpe, Stanground, Whittlesey, Thorney and Huntingdon all called to the incident.
The spokesman said there was no need for people to stay indoors around the incident, but residents are advised to avoid the area while emergency services are working.
Denise Lagerman, who lives near the fire, said; “I just saw the black smoke, and then teh flames were larger than the Brewers Select building. I have never seen anything like it.”
Crews now appear to have brought the fire under control, but are likely to remain at the scene for some time.
A Cambridgeshire police spokesman said: “We were called by the fire service at 1.10pm with reports of a fire on an industrial site in Fengate, Peterborough.
Police are in the area helping with traffic control in Fengate.
There is no mention of any injuries at this time.”
The fire is believed to have affected craft brewing specialist Brewers Select and car firm Evans Halshaw.
A spokesmen for both Brewers Select and Evans Halshaw made no comment when contacted by the Peterborough Telegraph.