Firefighters began tackling the fire at a plant for treating hazardous waste in Mortara, near the Lombard city of Pavia, at around 6:30am.
Black smoke clouds rose from the Eredi Bertè waste plant which were visible from several kilometres away. The plant itself, marked on the map below, is located two kilometres outside Mortara, home to around 16,000 people.
The mayor of Mortara advised local residents to stay inside and keep windows closed as a precautionary measure, and to avoid collecting produce grown in the area.
Local schools will also remain closed until at least Friday while environmental protection agency Arpa carries out analyses of the air quality to determine if dioxins or other toxic substances have been released. A bar in the affected area was also closed on Wednesday.
The prefect of Pavia, Attilio Visconti, told reporters: "The fire is under control but it will take many hours to tame it".
Waste depot fires are not uncommon in Italy: earlier this summer, one such blaze broke out near Venice shortly after two separate fires at scrapyards near Rome, one of which caused panic when smoke clouds were visible from the Vatican.
And the summer has seen a spate of wildfires brought on by an unusually dry spring followed by a heatwave, though police have blamed arsonists for many of the blazes.
Alessandra Mussolini, granddaughter of Benito. Photo: AFP