More than 30 firefighters were called to a transport company in Fitzgerald Road, Laverton North, just before 11am, after hydrofluoric acid leaked from a drum.
Hydrofluoric acid is highly corrosive and can immediately affect a person’s eyes, skin and lungs.
Emergency services were called as soon as the acid was found to be leaking from a drum at a factory owned by trucking company Toll Global Logistics.
Melbourne Fire Brigade said five firefighters and two members of the public have been taken to hospital due to effects of chemical fumes.
Hazmat technicians and a scientific adviser are on the scene as firefighters in breathing apparatus and gas suits deal with the spill.
Crews are going to be at the scene for some time.