An explosion at a chemical plant in Venice sent clouds of black smoke and flames into the sky on Friday.
The blast occurred in the Porto Marghera area on the mainland, a few kilometres from the historic centre of the lagoon city.
Firefighters said two people are believed to be injured.
Local authorities to order residents to stay inside and close doors and windows.
Ambulances and fire services were at the scene and television footage showed clouds of thick black smoke visible from several kilometres away.
The fire is spread across an area of some 10,000 square feet, firefighters said.
"The external emergency plan for the possible dispersion of chemicals into the environment has been activated," Vigili del Fuoco, Italy's fire and rescue service, said on Twitter.
Authorities said eight fire crews are at the scene, along with a Nuclear Biological Chemical-Radiological team.
