Heavyweight firefighting support from interstate will arrive on Saturday at a Melbourne recycling plant blaze, which is still burning out of control.
More than 100 firefighters spent a second night battling the massive inferno at SKM Recycling in Coolaroo after it started on Thursday morning.
During Saturday, two bulk water tankers and a turbine-aided firefighting robot will arrive from Fire Rescue NSW along with 10 crew.
The South Australian Metropolitan Fire Service has also deployed two tankers and a logistics vehicle and crew, along with two tankers and a command vehicle and crew from ACT Fire and Rescue.
Fire crew are expected to continue battling the blaze, which is contained within the perimeter of the plant, until Monday.
MFB confirmed it was putting foam on the fire in an effort to suppress smoke and hopes to make "significant inroads" during Saturday.
Thirty-eight trucks and about 130 firefighters have been working around the clock since the fire broke out in the stockpile of plastic, cardboard and paper.
Four people, including a four-year-old girl, have been hospitalised due to toxic smoke, while 15 people were assessed by paramedics on Friday.
Upfield train station and 115 homes in the nearby suburb of Dallas were evacuated on Thursday night when air quality levels dropped to very poor.
A change in conditions allowed people to return to their homes on Friday, although residents were advised to monitor warnings closely in case the situation changes.
The plant - which also caught fire in February, June and on Wednesday afternoon - was due to be inspected on Thursday over its fire management practices, Victoria's Environment Protection Authority said.
The cause of the blaze is not yet known but the MFB said it was not related to this week's earlier fire.
Acting deputy fire chief officer Ken Brown said the fire was particularly difficult to put out because it has penetrated bales of recyclables.
SKM Recycling declined to comment because the incident was under investigation.
Melbourne-based Maddens Lawyers flagged a possible class action against the factory's US-based owner-operator, SKM Industries.
A community relief centre has been set up at the Broadmeadows Aquatic and Leisure Centre.