Dozens of people are gearing up for a legal class action against a Melbourne recycling plant after a massive blaze choked their suburb with toxic smoke and caused ash to rain from the sky.
Firefighters have been battling the blaze at SKM Recycling at Coolaroo around the clock since Thursday, which is under control but continues to smoulder.
Crews will be on scene for several more days as they continue the slow task of breaking up bales of recyclables to douse the burning interior, a Metropolitan Fire Brigade spokeswoman said on Wednesday.
Upfield train station and 115 homes in the nearby suburb of Dallas were evacuated at the height of the blaze when air quality levels dropped to 'very poor'.
Four people, including a four-year-old girl, were hospitalised and many more were treated for smoke-related complaints caused by the mountains of burning plastic and paper.
Brendan Pendergast, from Maddens Lawyers, said there were possibly "several hundred people" affected by the fire, with about 70 so far joining the class action for compensation.
He hasn't yet put a value on the action.
"We are aware of scores of people who had to have medical attention and those problems are ongoing, with a significant impact on people's respiratory systems," Mr Pendergast told AAP.
"It's very early to say if there will be any long-term damage to people's health."
As well as health issues, residential properties were filled with soot, dust and ash, which has "infiltrated" ducted heating systems, curtains, carpets and gardens, Mr Pendergast added.
SKM said it is "extremely sorry for what our neighbours and the local community have gone through".
"The question of what happened and why has not been established and we will await the outcome of the various agency investigations underway," the company said in a statement on Wednesday.
SKM didn't comment on the class action and said its focus is working with authorities to prevent reignitions and minimising any further impacts
Mr Pendergast said there is "most certainly" a strong case considering the plant also caught fire in February, June and on the Wednesday afternoon before the blaze began.
"We are also told that on those previous occasions, there have been some people who also had to evacuate their houses," Mr Pendergast said.
"Whilst that didn't receive much publicity at the time, it is a significant factor that goes to our belief that their fire suppression systems were inadequate."
The site was due to be inspected for fire management practices on the day the latest blaze started.
Air quality monitoring stations near the site returned a 'very good' reading on Wednesday, according to the Environment Protection Authority.