Dozens of firefighters were unable to save a car parts factory which was destroyed by a fierce inferno overnight.

The blaze was first reported at Hyon All Parts on Sydney Road in Campbellfield at 8.47pm on Thursday.

It took 55 firefighters more than two hours to bring the fire under control, while gas cylinders exploded inside the factory and the roof of the building partially collapsed.

The damage bill for the fire is expected to reach many millions of dollars.