Vic factory fire causing heavy smoke

Heavy smoke from a fire at a grain storage facility is causing visibility issues for drivers on Melbourne's Princes Freeway.

The fire started on equipment in the factory and spread to grain being stored inside, a CFA spokesperson said on Tuesday morning.

The fire is under control, but drivers on the Princes Freeway and Avalon Road, Lara, have been urged to drive cautiously and turn on their headlights.