A Melbourne waste management factory that exploded into a fireball, spewing toxic smoke across the city’s northern suburbs on Friday, was storing three times the quantity of chemicals allowed.

The inferno at the Bradbury Industrial Services factory is continuing to burn this weekend, amid revelations its owner is linked to four other warehouses stocked with toxic waste.

Crews are working this weekend to manage the fire, which started about 6.40am on Friday.

Firefighters brought the blaze under control by midday on April 5, but it is expected to burn for days.

The Age reported early on Saturday that Bradbury Industrial Services controls illicit stockpiles of chemicals found at four other warehouses in March.

The Campbellfield factory had been storing almost three times the quantity of chemical permitted.

Victoria’s Environment Protection Authority last month suspended Bradbury Industrial Services’ licence to operate on March 15 after an inspection by officers.

The EPA’s executive director Damian Wells said the factory contained highly flammable materials.

“It was poor form by the duty holder. We suspended this licence in late March, we inspected the premises and found three times the amount of material being stored on the premise than it was licensed to store,” he said on Friday afternoon.

Storage containers were also inadequately labelled and being handled outside an appropriate area.

The factory is allowed to hold a maximum 150,000 litres of material, including solvents, inks, paints and other flammable materials before being processed.

It is suspended from taking more waste until it complies with licence requirements but can process what it already has.

The Campbellfield factory provided storage and disposal services for hazardous and industrial waste, and specialised in treating solvent and other waste from paint and related industries.

Melbourne Fire Brigade chief officer Dan Stephens confirmed authorities were “already aware of the site” at a press conference on Friday afternoon.

Mr Stephens said it was “fair to say” the incident had less of an impact on communities because of “site-specific plans” and cooperation between a raft of agencies.

“This situation now is far more controlled that when we first arrived,” Mr Stephens said.

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Mr Stephens said the blaze was on a similar scale to the West Footscray fire in August last year, which took authorities a day to get under control.

“So this is likely to be a protracted incident that will be ongoing for a number of days.

“(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.

Authorities have issued a watch and act alert and those in the Broadmeadows, Pascoe Vale and Coburg areas were urged to shelter indoors immediately.

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A witness from the nearby suburb of Wollert, Dave, told 3AW radio he saw a “massive explosion that looked like a mushroom cloud”.

The Department of Education and Training closed five state schools across Dallas and Broadmeadows as a “precautionary measure” on Friday. The schools listed included:

• Dallas Brooks Community Primary School
• Dallas North Primary School
• Broadmeadows Primary School
• Hume Central Secondary College
• Meadows Primary School

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People were urged to ensure all exterior doors, windows and vents were closed and heating and cooling systems turned off.

Crews found the 30-metre by 30-metre factory fully alight on arrival and quickly called for enforcements, authorities said.

It’s believed at least 30 people self-evacuated prior to fire crews arriving, according to the Metropolitan Fire Brigade.

Paramedics treated a man at the scene for an eye injury and he was taken to the Royal Eye and Ear Hospital in a stable condition.

Paramedics continued to remain at the scene throughout the morning, providing health support to the MFB.

Aerial appliances are tackling the fire from above, an MFB spokeswoman said.

Premier Daniel Andrews said there were no suspicious circumstances surrounding the blaze.

“There’s been an accident, something has gone wrong in terms of moving certain containers from one part of the facility to another,” he said.

EPA chief environmental scientist Andrea Hinwood said Merlynston creek had been contaminated and staff deployed to the scene will advise the incident controller about possible air monitoring and how to minimise impacts of the fire on local waterways.

-with AAP