Fire at an appliance factory near Treviso, northeastern Italy, unleashed thick smoke, including dioxin from burning plastic, into the air, the black cloud could be seen 30 kilometers away in Venice.
Venice officials sought to reassure people, saying in an advisory on its Web site that there were "no conditions of danger from the toxic cloud" for the city and the surrounding area.
The blaze broke out at a factory of De'Longhi SpA, a manufacturer of air conditioners, fans, heaters, coffee-makers and other appliances.
No major injuries were reported. A few people, complaining of irritation from the smoke, went to emergency rooms for treatment, Alessandro Barelli, director of Gemelli Polyclinic's poison control center in Rome, told SKY TG24 TV, adding that he was in contact with anti-poison experts near Treviso.
Col. Michele Sarno, commander of the Carabinieri police ecological dangers squad, said from the scene that dioxin was being unleashed into the air by the combustion of plastic material.
"The most important step to take is to close the windows and doors," Sarno told SKY. "It would be impossible to shut down the city," he said, adding there were no plans to evacuate Treviso, a city of about 80,000 people, and traffic was allowed to pass through the city.
SKY reported that local authorities banned outdoor sports activities while the fire continued to burn.
The choice of the city of Helsinki is not incidental as the capital of Finland had hosted US-Soviet negotiations on the limitation of nuclear stockpiles in 1969