Massive damage after Vic factory fire

A suspicious blaze that ripped through a Melbourne factory has been put out but not before it destroyed a dozen trucks and machinery.

The fire at the factory in Keilor East sent smoke billowing across the Calder Freeway and nearby homes on Wednesday morning, prompting a warning to residents to stay indoors.

The fire was brought under control about 6.45am, almost three hours after firefighters arrived on scene, but the property wasn't handed back to the owner till about 6pm.

A lack of available water nearby and the need to cut through a roller door to gain access to the factory hampered firefighters' early efforts to contain the blaze.

The owner of the business, which installs drains in new housing estates, says he was weeks away from moving the factory to another location.

"We were just about to move out and we've got a lot of money invested in the place," Heath Peatling told the Nine Network.

"I am still here, so I will start again."

The arson squad is investigating the cause of the fire.