Richard Matheson from the South Wales Fire and Rescue Service suggests that fire crews dealing with the blaze at the Vale Business Park may be on site for days.
The "deep-seated" fire involves a large amount of mixed recycling materials.
One of the owners of a soft furnishings business in the area was notified about the fire by one of her employees after they saw smoke from one of the buildings nearby.
Pam Owen, owner of Pam Owen's Soft Furnishings, has been in business for more than 25 years and is worried about the fire spreading.
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Western areas will see the wet and windy stuff continue overnight! And then tomorrow - i'm very sorry to say - there is more of it to come!
Dolaucothi Gold Mines is among five locations battling it out to be crowned Wales' best place in this year's Special Places competition.
It's the latest in a series of incidents, despite safety measures being put in place after the death of an off-duty police officer in March.