While Melbourne slept, MFB and CFA crews were hard at work battling a large fire in an industrial estate in Hoppers Crossing.
The blaze broke out in a complex of tilt slab factories in Graham Street just after midnight.
Crews arrived to find three out of four factories ablaze.
Firefighters used aerial appliances to attack the fire from above.
It took 50 firefighters an hour and forty five minutes to get the blaze under control.
MFB Fire Investigators have determined that the fire is suspicious and have referred the incident to Victoria Police for investigation.
Firefighters are expected to remain on scene for some time to ensure that the fire is fully extinguished.
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