A massive fire at a hazardous materials factory that is sending thick black smoke across Melbourne's north is likely to burn for days, authorities say.
More than 100 firefighters are battling the blaze in Thornycroft Street in Campbellfield, which ignited about 6.40am on Friday.
Nearby businesses have been evacuated and authorities have advised those in the Broadmeadows, Pascoe Vale and Coburg areas to stay indoors.
The address is registered to Bradbury Industrial Services, a toxic waste disposal company that had its licence suspended by the environment watchdog a fortnight ago for compliance issues.
MFB chief officer Dan Stephens said fire crews have managed to contain the blaze to the factory.
An LPG tank is stored nearby, but crews have measures in place to protect it, he said.
Mr Stephens said the incident is likely to last for days.
If you take the West Footscray fire to have been on a similar scale, that was the fire that occurred last year in August, it took us the best part of a day to get that fire under control. So this is likely to be a protracted incident that will be ongoing for a number of days," he told reporters.
A witness from the nearby suburb of Wollert, Dave, told 3AW radio he saw a "massive explosion that looked like a mushroom cloud".
Mr Stephens said the fire fight is "highly challenging" for crews.
"(With) the nature of the hazardous materials in the premise, flammable liquids, we do have a number of running fuel fires which has caused the fire to spread beyond the premise. But we've managed to contain that," he said.
The fire is sending a large volume of black smoke towards the CBD and witnesses have reported seeing plumes as far as Clayton and Coldstream.
People are urged to ensure all exterior doors, windows and vents are closed and heating and cooling systems are turned off.
Mr Stephens said the MFB and other agencies are aware of the factory but what is inside is still being established.
About 30 people self evacuated before fire crews arrived to find the 30-metre by 30-metre factory fully alight.
One man was taken to the Royal Eye and Ear Hospital for an eye injury.
Paramedics remain at the scene, as aerial appliances tackle the fire from above.
Environment Protection Authority staff are also at the scene.
