A huge factory blaze in Melbourne's north has been brought under control.

The blaze broke out at the scrap metal factory in Bolinda Road, Campbellfield, shortly after 11.30am.

It took firefighters around two hours to bring the inferno under control.

It is understood two men were treated for burns.

The MFB warned nearby residents to stay indoors, and close doors, windows and vents.

Nearby factory workers were also evacuated.

A plume of thick black smoke is hovering over the Glenroy, Fawkner, and Coburg areas and is understood to be heading towards the city.