The fire is believed to involve a carpet and flooring business, piano and business supplies units on the Tiverton Business Park opposite B&M and next to McDonalds.
People in nearby local businesses have been evacuated.
Devon and Somerset Fire and Rescue Service said it received the first call to attend at 6.42pm tonight, Monday, January 2.
DSFRS said that 12 fire engines plus specialist appliances including two aerial ladder platforms and high volume pumps were sent to the scene.
It is unknown how the fire started.
It is not known if anyone is injured.
Loud bangs have been heard coming from the scene.
A 150 metre police cordon has been put in place for public safety and ambulance personnel are also at the scene.
Huge flames and clouds of smoke could be seen.
Devon and Somerset Fire and Rescue said that firefighters are continuing to tackle the fire to try to prevent it spreading to neighbouring properties.
It is expected that the incident will be ongoing throughout the night.
Fire crews in attendance are South Molton, Danes Castle (Exeter), Bampton, Crediton, Cullompton, Tiverton, Witheridge, Middlemoor (Exeter), Urban Search and Rescue, Taunton, Bridgwater, Wellington and Wiveliscombe.