Managing director Jan Smith told the Scunthorpe Telegraph: "Somebody has been in and torched our machines.”
He added: "I have no idea why somebody would do this this. I am absolutely gutted with it. In the short term we can't do anything. We will get back on our feet though, although we will be putting extra security in place."
He said that seven machines were torched, including a dumper truck, a loading shovel and two large crushing plants, equating to nearly £600,000 worth of damage in total.