Fire crews attended a first at a recycling plant in Broadmeadows on Sunday.
Multiple calls to triple-0 were made about 5.20am with the plant on Maygar Boulevard alight.
Crews arrived to find a 20 metre by 50 metre steel shed and a further area well alight.
There are no persons in the buildings.
There is a large volume of smoke to the north and a community warning for smoke in the area was issued.
Aerial appliances were used to help put out the fire, which was deemed under control by 7.44am.
Police, Yarra Valley Water and the Environment Protection Authority all attended.
The EPA, which is investigating the fire, conducted testing on Merlynston Creek with concerns some run off may have entered the creek.
