Russell Meredith, 36, operations director at Ravensbourn factory and his father David Meredith, 74, who is a co-owner of the firm, said the fire started after midnight when three people were still in the factory.
A massive fire sparked a "firenado" in the English Midlands on Tuesday.
A blaze turned into a tornado-like whirl as firefighters worked to extinguish a fire at a plastics factory in Derbyshire, England.
Firefighters were joined by colleagues from other counties as they tried to prevent the fire spreading.
The 50-feet (15.2m) high whirling phenomenon was filmed by emergency services personnel while they attended a fire at a plastic-pallet factory in Albert Village in the early hours of Wednesday morning.
China says no to Winnie the Pooh film over comparisons with president
The only other Disney film this year to receive a no-go from China was sci-fi film " A Wrinkle in Time ". With one particular image comparing President Xi to Winnie and President Obama to Tigger.
In the horrifying footage, the "firenado" is seen swirling as firefighters rushed to the scene.
Video uploaded to the Leicestershire Fire and Rescue Service Facebook page showed the rare fire tornado, also known as a fire whirl, stretching into the sky from a large plastic-pallets fire.
The black smoke could be seen in Shepshed in Leicestershire and Nottingham city centre. While there had been three employees in the building at the time of the fire, no injuries were reported.
"While the site of the fire is not directly next to any residential properties, we are still advising locals to keep their windows and doors closed until the fire is completely out and the smoke has subsided".