The South Yorkshire Fire and Rescue (SYFR) officer investigating the cause of the inferno which devasated an Hexthorpe industrial unit on Tuesday said it is believed to have been started accidentally.
Over 40 firefighters spent 10 hours tackling the blaze, which started at an unit in Albion Terrace at 8am.
The blaze is thought to have started at a bio-diesel firm named locally as Ample Fuel, but quickly spread to neighbouring business The Stuffing Plant, which specialises in stuffing large volumes of toys, teddies and bean bags.
The buildings have been described by an official at the site as ‘write-offs’.
Trains between Doncaster and Sheffield were stopped for around eight hours because the fire was so close to the railway lines.
A SYFR spokesman said: “The investigation is still ongoing at this point in time but it is believed to be an accidental fire.”